Tungsten feature fill

ABSTRACT

Described herein are methods of filling features with tungsten and related systems and apparatus. The methods include inside-out fill techniques as well as conformal deposition in features. Inside-out fill techniques can include selective deposition on etched tungsten layers in features. Conformal and non-conformal etch techniques can be used according to various implementations. The methods described herein can be used to fill vertical features, such as in tungsten vias, and horizontal features, such as vertical NAND (VNAND) word lines. Examples of applications include logic and memory contact fill, DRAM buried word line fill, vertically integrated memory gate/word line fill, and 3-D integration with through-silicon vias (TSVs).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 14/502,817, filed Sep. 30, 2014, which is acontinuation of U.S. application Ser. No. 13/851,885, filed Mar. 27,2013, which claims the benefit of priority under 35 USC §119(e) of U.S.Provisional Patent Application No. 61/616,377, filed Mar. 27, 2012, bothof which are incorporated herein by this reference for all purposes.

BACKGROUND

Deposition of tungsten-containing materials using chemical vapordeposition (CVD) techniques is an integral part of many semiconductorfabrication processes. These materials may be used for horizontalinterconnects, vias between adjacent metal layers, contacts betweenfirst metal layers and devices on the silicon substrate, and high aspectratio features. In a conventional deposition process, a substrate isheated to a predetermined process temperature in a deposition chamber,and a thin layer of tungsten-containing material that serves as a seedor nucleation layer is deposited. Thereafter, the remainder of thetungsten-containing material (the bulk layer) is deposited on thenucleation layer. Conventionally, the tungsten-containing materials areformed by the reduction of tungsten hexafluoride (WF₆) with hydrogen(H₂). Tungsten-containing materials are deposited over an entire exposedsurface area of the substrate including features and a field region.

Depositing tungsten-containing materials into small and high aspectratio features may cause formation of seams and voids inside the filledfeatures. Large seams may lead to high resistance, contamination, lossof filled materials, and otherwise degrade performance of integratedcircuits. For example, a seam may extend close to the field region afterfilling process and then open during chemical-mechanical planarization.

SUMMARY

One aspect of the subject matter described in this disclosure can beimplemented in a method of filling a feature with tungsten includingconformally depositing tungsten in the feature to fill the feature witha first bulk tungsten layer, removing a portion of the first bulktungsten layer to leave an etched tungsten layer in the feature; andselectively depositing a second bulk tungsten layer on the etchedtungsten layer. According to various implementations, the second bulktungsten layer may fill the feature, or one or more additional tungstenlayers may be selectively or conformally deposited to complete featurefill. In some implementations, the second bulk tungsten layer maypartially fill the feature with the remaining portion of the featureleft unfilled.

According to various implementations, conformally filling the featurewith the first tungsten bulk layer may include allowing one or morevoids and/or seams to be formed in the feature. One or more of the seamsand/or voids can be removed or opened when removing a portion of thedeposited tungsten layer.

Selectively depositing the second tungsten bulk layer can involvedeposition directly on the etched tungsten layer without forming anucleation layer in the feature. In some implementations, the directionand/or length of grain growth in the second bulk tungsten layer differsfrom that of the first bulk tungsten layer.

According to various implementations, the feature may bevertically-oriented or horizontally-oriented with reference to the planeof the substrate. In some implementations, the feature may include oneor more constrictions or overhangs, and/or have a re-entrant profile.Examples of constrictions include pillar constrictions in a 3-Dstructure. Removing a portion of the first bulk tungsten layer caninclude etching past a constriction or overhang.

The first bulk tungsten layer may be deposited on a feature surface,including on a dielectric surface, on an under-layer lining the feature,or on a previously deposited tungsten nucleation layer or bulk tungstenlayer. Examples of under-layers include titanium (Ti), titanium nitride(TiN), tungsten nitride (WN), fluorine-free tungsten (FFW), and TiAl(titanium aluminide).

Removing a portion of the first tungsten bulk layer can include exposingthe layer to activated species generated in a plasma generator,including those generated in a remotely-generated and/or in-situgenerated plasma. Examples of plasma generators that may be used includecapacitively coupled plasma (CCP) generators, inductively coupled plasma(ICP) generators, transformer coupled plasma (TCP) generators, electroncyclotron resonance (ECR) generators, and helicon plasma generators.Examples of activated species can include ions, radicals and atomicspecies. In some implementations, the methods can include exposing thetungsten to radical and atomic species with substantially no ionicspecies present. In some other implementations, the methods can includeexposing the tungsten to ionic species.

In some implementations, the feature is filled with tungsten having astep coverage of over 100%. In some implementations, the second bulklayer of tungsten may be non-conformal to the feature.

Another aspect of the subject matter described herein can be implementedin methods of filling a feature with tungsten that involve providing asubstrate including a feature having one or more feature openings,feature sidewalls, a feature interior, and a feature axis extendingalong the length of the feature, depositing tungsten in the feature tofill the feature with a first bulk tungsten layer, wherein grain growthis substantially orthogonal to the feature axis; removing a portion ofthe first bulk tungsten layer to leave an etched tungsten layer in thefeature; and selectively depositing a second bulk tungsten layer on theetched tungsten layer, wherein grain growth is substantially parallel tothe feature axis.

Another aspect of the subject matter described herein can be implementedin methods that involve conformally depositing tungsten in the featureto fill the feature with a first bulk tungsten layer, receiving thesubstrate after a portion of the tungsten is removed, the receivedfeature including an etched tungsten layer; and selectively depositing asecond bulk tungsten layer on the etched tungsten layer. In someimplementations, the second bulk tungsten layer can be non-conformal tothe feature.

Another aspect of the subject matter described herein can be implementedin methods that involve receiving a substrate including a feature havinga feature opening, feature sidewalls, and a closed feature end, thefeature filled with a conformal bulk tungsten layer including a voidand/or seam formed in the conformal bulk tungsten layer; and etching aportion of the conformal tungsten bulk layer, including removingtungsten from the sidewalls of the feature such that tungsten remainsonly substantially at the closed end of the feature.

Another aspect of the subject matter described herein can be implementedin methods that involve receiving a substrate including a feature havinga feature opening, feature sidewalls, and a closed feature end, thefeature filled with a conformal bulk tungsten layer including a voidand/or seam formed in the conformal bulk tungsten layer; and etching aportion of the conformal tungsten bulk layer, including removingtungsten from the sidewalls of the feature such that tungsten remainsonly substantially in the feature interior.

Another aspect of the subject matter described herein can be implementedin methods that involve providing a substrate including a feature havingone or more feature openings, feature sidewalls, and a feature interior,depositing a first bulk tungsten layer in the feature; etching the firstbulk tungsten layer to form an etched tungsten layer, wherein etchingthe first bulk tungsten layer includes removing substantially alltungsten in the feature up to a recess depth extending from the one ormore feature openings; and depositing a second bulk tungsten layer inthe feature.

According to various implementations, the first bulk layer may wholly orpartially fill a feature. In some implementations, a void or seam may beformed in the first bulk layer. In some implementations, etching thefirst bulk layer includes lateral etching of at least a region of thefirst bulk layer. The second bulk layer may be selectively orconformally deposited in the feature.

Another aspect of the subject matter described herein can be implementedin methods that involve conformally depositing a boron layer in thefeature; converting a portion of the boron layer in the feature totungsten, leaving a remaining boron layer in the feature; selectivelyetching the tungsten without etching the remaining boron layer; andconverting the remaining boron layer to tungsten.

Another aspect of the subject matter described herein can be implementedin methods that involve conformally depositing a boron layer in thefeature, the boron layer having a thickness of at least about 5 nm;converting the entire thickness of the boron layer feature to tungstensuch that the filled portion of the feature undergoes volumetricexpansion; and repeating the conformal deposition and conversionoperations one or more times to partially or wholly fill the featurewith tungsten.

Another aspect of the subject matter described herein can be implementedin methods that involve conformally depositing a fluorine-free tungstennitride layer in the feature; and converting the fluorine tungstennitride layer to a fluorine-free tungsten layer.

Yet another aspect of the subject matter described herein can beimplemented in methods that involve conformally depositing a tungstenlayer in the feature using a halogen-containing reducing agent; pumpingout halogen-containing byproducts; and depositing a fluorine freetungsten-containing on the conformal tungsten layer.

Further aspects can be implemented in apparatus configured to implementany of the methods described herein.

These and other aspects are described further with reference to theFigures.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1G show examples of various structures that can be filled withtungsten-containing materials according to the processes describedherein.

FIGS. 2 and 2A are process flow diagrams illustrating certain operationsin methods of inside-out fill of features with tungsten.

FIGS. 3A-4B are schematic representations of features at various stagesof inside-out feature fill.

FIGS. 5A-5D are graphs illustrating tungsten (W), titanium (Ti) andtitanium nitride (TiN) etch rates and etch selectivities at varioustemperatures.

FIG. 6 is a schematic representation of a feature including a recessetched tungsten layer.

FIG. 7 is a schematic representation of a feature at various stages ofrecess etching.

FIG. 8 is a schematic representation of a feature at various stages offeature fill employing a recess etch.

FIG. 9A is a schematic representation of features at various stages ofetching that illustrates etch conformality modulation.

FIG. 9B is a graph showing tungsten etch rate as a function of etchtemperature for different etchant flows.

FIG. 10 is a schematic representation of a feature at various stages offeature fill employing a non-conformal etch.

FIG. 11 is a schematic representation of a feature at various stages offeature fill employing selective inhibition of tungsten nucleation.

FIG. 12 is a graph showing time bulk layer growth delay for filmsdeposited after high and low power etches.

FIG. 13A is a schematic representation of a feature at various stages offeature fill employing boron conversion to tungsten.

FIG. 13B is a process flow diagram illustrating certain operations inmethods of filling features using partial conversion of boron totungsten.

FIGS. 13C and 13D are process flow diagram illustrating certainoperations in methods of filling features using fluorine-freetungsten-containing layers.

FIGS. 14-23 are schematic representations of three-dimensional verticalNAND (3-D VNAND) features at various stages of feature fill.

FIGS. 24-25B are schematic diagrams showing examples of apparatussuitable for practicing the methods described herein.

DETAILED DESCRIPTION OF EXAMPLE IMPLEMENTATIONS

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Thepresent invention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail to not unnecessarily obscure the present invention.While the invention will be described in conjunction with the specificimplementations, it will be understood that it is not intended to limitthe invention to the implementations.

Described herein are methods of filling features with tungsten andrelated systems and apparatus. Examples of application include logic andmemory contact fill, DRAM buried wordline fill, vertically integratedmemory gate/wordline fill, and 3-D integration with through-silicon vias(TSVs). The methods described herein can be used to fill verticalfeatures, such as in tungsten vias, and horizontal features, such asvertical NAND (VNAND) wordlines. The methods may be used for conformaland bottom-up or inside-out fill.

According to various implementations, the features can be characterizedby one or more of narrow and/or re-entrant openings, constrictionswithin the feature, and high aspect ratios. Examples of features thatcan be filled are depicted in FIGS. 1A-1C. FIG. 1A shows an example of across-sectional depiction of a vertical feature 101 to be filled withtungsten. The feature can include a feature hole 105 in a substrate 103.The substrate may be a silicon wafer, e.g., a 200-mm wafer, a 300-mmwafer, or a 450-mm wafer, including wafers having one or more layers ofmaterial such as dielectric, conducting, or semi-conducting materialdeposited thereon. The feature may be formed in one or more of theselayers. For example, the feature may be formed at least partially in adielectric layer. In some implementations, the feature hole 105 may havean aspect ratio of at least about 2:1, at least about 4:1, at leastabout 6:1 or higher. The feature hole 105 may also have a dimension nearthe opening, e.g., an opening diameter or line width, of between about10 nm to 500 nm, for example between about 25 nm to 300 nm. The featurehole 105 can be referred to as an unfilled feature or simply a feature.The feature 101, and any feature, may be characterized in part by anaxis 118 that extends through the length of the feature, withvertically-oriented features having vertical axes andhorizontally-oriented features having horizontal axes.

FIG. 1B shows an example of a feature 101 that has a re-entrant profile.A re-entrant profile is a profile that narrows from a bottom, closedend, or interior of the feature to the feature opening. According tovarious implementations, the profile may narrow gradually and/or includean overhang at the feature opening. FIG. 1B shows an example of thelatter, with an under-layer 113 lining the sidewall or interior surfacesof the feature hole 105. The under-layer 113 can be for example, adiffusion barrier layer, an adhesion layer, a nucleation layer, acombination of thereof, or any other applicable material. Non-limitingexamples of under-layers can include dielectric layers and conductinglayers, e.g., silicon oxides, silicon nitrides, silicon carbides, metaloxides, metal nitrides, metal carbides, and metal layers. In particularimplementations an under-layer can be one or more of Ti, TiN, WN, TiAl,and W. The under-layer 113 forms an overhang 115 such that theunder-layer 113 is thicker near the opening of the feature 101 thaninside the feature 101.

In some implementations, features having one or more constrictionswithin the feature may be filled. FIG. 1C shows examples of views ofvarious filled features having constrictions. Each of the examples (a),(b) and (c) in FIG. 1C includes a constriction 109 at a midpoint withinthe feature. The constriction 109 can be, for example, between about 15nm-20 nm wide. Constrictions can cause pinch off during deposition oftungsten in the feature using conventional techniques, with depositedtungsten blocking further deposition past the constriction before thatportion of the feature is filled, resulting in voids in the feature.Example (b) further includes a liner/barrier overhang 115 at the featureopening. Such an overhang could also be a potential pinch-off point.Example (c) includes a constriction 112 further away from the fieldregion than the overhang 115 in example (b). As described further below,methods described herein allow void-free fill as depicted in FIG. 1C.

Horizontal features, such as in 3-D memory structures, can also befilled. FIG. 1D shows an example of a horizontal feature 150 thatincludes a constriction 151. For example, horizontal feature 150 may bea word line in a VNAND structure.

In some implementations, the constrictions can be due to the presence ofpillars in a VNAND or other structure. FIG. 1E, for example, shows aplan view of pillars 125 in a VNAND or vertically integrated memory(VIM) structure 148, with FIG. 1F showing a simplified schematic of across-sectional depiction of the pillars 125. Arrows in FIG. 1Erepresent deposition material; as pillars 125 are disposed between anarea 127 and a gas inlet or other deposition source, adjacent pillarscan result in constrictions 151 that present challenges in void freefill of an area 127.

The structure 148 can be formed, for example, by depositing a stack ofalternating interlayer dielectric layers 154 and sacrificial layers (notshown) on a substrate 100 and selectively etching the sacrificiallayers. The interlayer dielectric layers may be, for example, siliconoxide and/or silicon nitride layers, with the sacrificial layers amaterial selectively etchable with an etchant. This may be followed byetching and deposition processes to form pillars 125, which can includechannel regions of the completed memory device.

The main surface of substrate 100 can extend in the x and y directions,with pillars 125 oriented in the z-direction. In the example of FIGS. 1Eand 1F, pillars 125 are arranged in an offset fashion, such that pillars125 that are immediately adjacent in the x-direction are offset witheach other in the y-direction and vice versa. According to variousimplementations, the pillars (and corresponding constrictions formed byadjacent pillars) may be arranged in any number of manners. Moreover,the pillars 125 may be any shape including circular, square, etc.Pillars 125 can include an annular semi-conducting material, or circular(or square) semi-conducting material. A gate dielectric may surround thesemi-conducting material. The area between each interlayer dielectriclayer 129 can be filled with tungsten; thus structure 148 has aplurality of stacked horizontally-oriented features that extend in the xand/or y directions to be filled.

FIG. 1G provides another example of a view horizontal feature, forexample, of a VNAND or other structure including pillar constrictions151. The example in FIG. 1G is open-ended, with material to be depositedable to enter horizontally from two sides as indicated by the arrows.(It should be noted that example in FIG. 1G can be seen as a 2-Drendering 3-D features of the structure, with the FIG. 1G being across-sectional depiction of an area to be filled and pillarconstrictions shown in the figure representing constrictions that wouldbe seen in a plan rather than cross-sectional view.) In someimplementations, 3-D structures can be characterized with the area to befilled extending along two or three dimensions (e.g., in the x and y orx, y and z-directions in the example of FIG. 1F), and can present morechallenges for fill than filling holes or trenches that extend along oneor two dimensions. For example, controlling fill of a 3-D structure canbe challenging as deposition gasses may enter a feature from multipledimensions.

Filling features with tungsten-containing materials may cause formationof voids and seams inside the filled features. A void is region in thefeature that is left unfilled. A void can form, for example, when thedeposited material forms a pinch point within the feature, sealing offan unfilled space within the feature preventing reactant entry anddeposition.

There are multiple potential causes for void and seam formation. One isan overhang formed near the feature opening during deposition oftungsten-containing materials or, more typically, other materials, suchas a diffusion barrier layer or a nucleation layer. An example is shownin FIG. 1B.

Another cause of void or seam formation that is not illustrated in FIG.1B but that nevertheless may lead to seam formation or enlarging seamsis curved (or bowed) side walls of feature holes, which are alsoreferred to as bowed features. In a bowed feature the cross-sectionaldimension of the cavity near the opening is smaller than that inside thefeature. Effects of these narrower openings in the bowed features aresomewhat similar to the overhang problem described above. Constrictionswithin a feature such as shown in FIGS. 1C, 1D and 1G also presentchallenges for tungsten fill without few or no voids and seams.

Even if void free fill is achieved, tungsten in the feature may containa seam running through the axis or middle of the via, trench, line orother feature. This is because tungsten growth can begin at the sidewalland continues until the grains meet with tungsten growing from theopposite sidewall. This seam can allow for trapping of impuritiesincluding fluorine-containing compounds such as hydrofluoric acid (HF).During chemical mechanical planarization (CMP), coring can alsopropagate from the seam. According to various implementations, themethods described herein can reduce or eliminate void and seamformation. The methods described herein may also address one or more ofthe following:

1) Very challenging profiles: Void free fill can be achieved in mostre-entrant features using dep-etch-dep cycles as described in U.S.patent application Ser. No. 13/351,970, incorporated by referenceherein. However, depending on the dimensions and geometry, multipledep-etch cycles may be needed to achieve void-free fill. This can affectprocess stability and throughput. Implementations described herein canprovide feature fill with fewer or no dep-etch-dep cycles.

2) Small features and liner/barrier impact: In cases where the featuresizes are extremely small, tuning the etch process without impacting theintegrity of the underlayer liner/barrier can be very difficult. In somecases intermittent Ti attack—possibly due to formation of a passivatingTiFx layer during the etch—can occur during a W-selective etch.

3) Scattering at W grain boundaries: Presence of multiple W grainsinside the feature can result in electron loss due to grain boundaryscattering. As a result, actual device performance will be degradedcompared to theoretical predictions and blanket wafer results.

4) Reduced via volume for W fill: Especially in smaller and newerfeatures, a significant part of the metal contact is used up by the Wbarrier (TiN, WN etc.). These films are typically higher resistivitythan W and negatively impact electrical characteristics like contactresistance etc.

Provided herein are various methods of filling features with tungstenthat reduce or eliminate void and seam formation. The methods may beused for feature fill of features of any orientation, including verticaland horizontal orientations. In some implementations, the methods may beused to fill features having an angled orientation with respect to theplane of the substrate. In some implementations, the methods may be usedto fill a feature having multiple orientations. Examples of suchfeatures include 3-D features in which deposition gasses may enter afeature vertically and laterally. Further, in some implementations, themethods may be used to fill multiple features of different orientationson a single substrate.

Examples of feature fill for horizontally-oriented andvertically-oriented features are described below. It should be notedthat in most cases, the examples applicable to bothhorizontally-oriented or vertically-oriented features. Moreover, itshould also be noted that in the description below, the term “lateral”may be used to refer to a direction generally orthogonal to the featureaxis and the term “vertical” to refer to a direct generally along thefeature axis.

While the description below focuses on tungsten feature fill, aspects ofthe disclosure may also be implemented in filling features with othermaterials. For example, feature fill using one or more techniquesdescribed above of inside-out feature fill, etch conformalitymodulation, reducing agent conversion, partial reducing agent conversionwith the unconverted reducing agent used as an etch stop, andhalogen-free fill may be used to fill features with other materialsincluding other tungsten-containing materials (e.g., tungsten nitride(WN) and tungsten carbide (WC)), titanium-containing materials (e.g.,titanium (Ti), titanium nitride (TiN), titanium silicide (TiSi),titanium carbide (TiC) and titanium aluminide (TiAl)),tantalum-containing materials (e.g., tantalum (Ta), and tantalum nitride(TaN)), and nickel-containing materials (e.g., nickel (Ni) and nickelsilicide (NiSi).

Inside-Out Fill

Conventional tungsten deposition in a re-entrant feature starts from asidewall surface and progresses laterally (i.e., orthogonal to thesidewall surface and feature axis) until the feature is pinched off.With the inside-out fill described herein, tungsten growth progressesvertically (i.e., along the feature axis) from with the feature. In someimplementations, tungsten growth from feature sidewalls is eliminated ordelayed, allowing tungsten to grow from the inside-out. This can resultin large tungsten grains and lower resistivity, no seam down the featureaxis and reducing coring during chemical mechanical planarization (CMP),eliminating and reducing voids in the feature.

Implementations described herein can involve deposition of a tungsten ina feature, followed by an etch to remove all or some of the tungstendeposited on the sidewalls while leaving tungsten further within thefeature, e.g., at a closed end of a feature such as on the bottom of avertically-oriented feature or at a closed end of ahorizontally-oriented feature, or in the interior of ahorizontally-oriented feature having multiple openings. The initialdeposition may be conformal with the tungsten growing evenly from allaccessible surfaces of the feature. A subsequent deposition then can be“selective” in that the tungsten preferentially grows on the tungstenremaining in the feature, rather than on an under-layer or substratestructure. In some implementations, the overall deposition process(e.g., conformal deposition—etch—selective deposition) can becharacterized as inside-out rather than conformal. Inside-out fillrefers to the growth occurring from the interior of the feature, and maybe termed “bottom-up” fill for vertical closed-ended structures, such asin FIGS. 1A and 1B.

FIG. 2 is a process flow diagram illustrating certain operations of amethod of inside-out feature fill. The method can begin with conformallydepositing tungsten in a feature in block 201. In some implementations,block 201 can involve deposition of a tungsten nucleation layer,followed by bulk deposition. Tungsten nucleation layer deposition andbulk deposition techniques are described further below. In someimplementations, block 201 may involve only bulk deposition, if forexample, the feature includes an under-layer that supports tungstendeposition. In features that include constrictions or are otherwisesusceptible to pinch-off, block 201 can be performed at least until thefeature is pinched off. In conformal deposition, deposition starts fromeach surface and progresses with growth generally orthogonal to thesurface. Tungsten growth in features starts from each sidewall andprogresses until the growth pinches off the feature. In someimplementations, the amount of tungsten deposited block 201 can bedetermined based on the narrowest feature dimension. For example, if thenarrowest dimension is 50 nm, a CVD reaction in block 201 can be allowedto run long enough to deposit 25 nm on each surface, at which point thedeposited tungsten blocks further reactant diffusion into the feature.This can generally be determined prior to the reaction based on thereaction kinetics, tungsten nucleation layer thickness, etc. In someimplementations, block 201 can involve multiple dep-etch-dep cycles asdescribed in U.S. patent application Ser. No. 13/016,656, incorporatedby reference herein. In some implementations, block 201 does not includeany etch operations, with just a deposition until at least the featureis pinched off. Block 201 can occur in a single chamber, a singlestation of a multi-station or single station chamber, in multiplestations of multi-station apparatus, or in multiple chambers. Forexample, block 201 can involve tungsten nucleation layer deposition inone station of a chamber, followed by bulk deposition in another stationof the chamber.

The process can continue with a partial etch of tungsten in a block 203.Some tungsten remains in the feature, but the etch removes tungsten fromat least some of the sidewalls of the feature. Block 203 generallyinvolves a chemical etch, with for example, fluorine-containing speciesor other etchant species. In some implementations, activated species maybe used. Activated species can include atomic species, radical species,and ionic species. For the purposes of this application, activatedspecies are distinguished from recombined species and from the gasesinitially fed into a plasma generator. For example, partially etchingthe deposited tungsten can involve exposure to etchant species generatedin a remote or in-situ plasma generator. In some implementations, bothremotely-generated and in-situ generated plasma species may be used,either sequentially or concurrently. In some implementations, anon-plasma chemical etch using F₂, CF₃Cl, or other etchant chemistry maybe used. Block 203 may occur in the same chamber as block 201 or in adifferent chamber. Methods of etching tungsten in a feature aredescribed further below. Depending on the feature architecture, the etchmay be conformal or non-conformal. Further, the etch back may progressgenerally laterally (orthogonal to the feature axis) and/or vertically(along the feature axis).

According to various implementations, the etch may be preferential ornon-preferential to an under-layer. For example, an etch can bepreferential to W with, for example, a Ti or TiN under-layer acting asan etch stop. In some implementations, the etch can etch W and Ti or TiNwith an underlying dielectric acting as an etch stop.

The process then continues at block 205 with selective deposition on theremaining tungsten. Selective deposition refers to preferentialdeposition on the tungsten surfaces with respect to the sidewall orother surfaces from which tungsten is removed. In some implementations,the selective deposition process may deposit substantially no tungstenon the sidewall surfaces. In some implementations, the selectivedeposition process may deposit a small amount of tungsten on thesidewalls surfaces, though at significantly slower growth rate thandeposition on the tungsten surfaces. For example, growth rate anddeposited thickness may be half as much or less on the sidewall surfacesthan on the tungsten surfaces. In some implementations, it may be atenth or even a hundredth as much.

In some implementations, block 205 may proceed without deposition of anucleation layer. This can allow selective deposition only on theremaining tungsten in the feature. In many implementations, block 201will involve deposition of a nucleation layer to achieve conformaldeposition, while block 205 proceeds with deposition on the etchedtungsten layer without an intermediate nucleation layer deposition. Insome implementations, a nucleation layer may be deposited on at leastthe portion of the feature on which further growth is desired. If anucleation layer is deposited in block 205 including on sidewall orother surfaces where subsequent deposition is not desired, tungstennucleation on those surfaces can be selectively inhibited. Methods ofinhibiting tungsten nucleation in features are described in U.S. patentapplication Ser. No. 13/774,350, incorporated by reference herein.

FIG. 2A is a process flow illustrating certain operations in an exampleof inside-out fill according to FIG. 2. The process can begin bysequentially pulsing a tungsten-containing precursor and one or morereducing agents to form a tungsten nucleation layer by an atomic layerdeposition (ALD) or pulsed nucleation layer (PNL) process (201 a). Athin conformal nucleation layer that can support subsequent bulkdeposition is formed. Further description of nucleation layer depositionis provided below. Next, a tungsten-containing precursor and a reducingagent are simultaneously introduced to a chamber housing the feature(201 b). This results in deposition of a bulk layer of tungsten bychemical vapor deposition (CVD) on the tungsten nucleation layer formedin block 201 a. The bulk tungsten layer follows the contours of theunderlying tungsten nucleation layer, which follows the contours of thefeature, for conformal deposition. The tungsten is then partially etched(203) as described above with reference to FIG. 2. The process continuesby again simultaneously introducing a tungsten-containing precursor anda reducing agent to deposit another bulk layer by CVD (205 a). In theexample of FIG. 2A, the bulk tungsten layer deposited in block 205 a isdeposited directly on the etched tungsten without formation of anothernucleation layer.

In some implementations, feature fill can involve conformal tungstendeposition to fill a feature, allowing the deposition to proceed evenwith the formation of a void or seam within the feature, followed byetch back to open the feature, and selective deposition in the feature.According to various implementations the conformal deposition to fillthe feature may include fill to the top of the feature or only through aconstriction or pinch point. In either case, a portion of the featureincluding a seam and/or void may be closed off to further depositionprior to etch back.

Previous schemes involved a partial fill during a first depositionoperation leaving the via or other feature open and not closed off.During a subsequent etch step, in these schemes, subsequent etchingtargeted at tungsten removal in the field and pinch point could have theunwanted side effect of removing the tungsten inside the via or otherfeature. Then, a subsequent deposition step could regrow tungsten at thesame rate inside the via or other feature and at the pinch point,resulting in the same keyhole void as a deposition-only feature fill. Bycontrast, the methods described herein can leave partial growth withinthe feature, with the partial growth resulting in selective depositionin a subsequent deposition operation. For example, a process can involveetching a pinched-off via to completely remove tungsten from the fieldand pinch point, leaving partial tungsten growth inside the via intact.A subsequent tungsten deposition allows tungsten regrowth inside the viaon the existing tungsten layer, while a significant growth delay in thefield prevents pinch-off and voids in the final via fill. As discussedabove, the significant growth delay may be due at least in part to theremoval of a surface that supports tungsten growth. In someimplementations, the etch may be preferential to tungsten with respectto an under-layer. For example, feature including a TiN/W (titaniumnitride under-layer/tungsten layer) bilayer may be subjected to an etchpreferential to tungsten. The preferential etch (also referred to as aselective etch) may remove tungsten from the field and pinch pointwithout etching through the TiN at the field and pinch point. Subsequentdeposition allows tungsten regrowth inside the feature, but not on thefield or on the sidewalls of the pinch point. As a result, the growth isinside-out (e.g., bottom-up) rather than conformal. Variousimplementations are described below with respect to FIGS. 3A, 3B, 4A and4B.

In some implementations, feature fill can involve 1) deposition to pinchoff a feature; 2) etch-back to remove tungsten through the pinch point;3) fill by selective deposition below the pinch-point; and 4) fill theremainder of the feature. In some implementations (2) involves etchingconditions selective (i.e., preferential) to tungsten over a TiN, Ti, orother under-layer. FIG. 3A shows an example of cross-sectional schematicdepictions of a feature fill using such a method. First, a feature 301including a pinch point 351 and a TiN under-layer 313 is filled using aconformal deposition technique at an operation 310. Deposition isallowed to continue such that the feature is pinched off, with tungstendeposited on the field region 317 as well. Deposition in this operationmay be generally conformal to the feature, leaving void 312 in thefilled feature 301. An example of conformal deposition is depictedschematically in FIG. 3C, in which illustrates tungsten growth stages350, 360, and 370 in a feature 301. Stages 350, 360, and 370 mayrepresent stages in a progression of a CVD process of depositingtungsten in feature 301, for example. At stage 350, a tungsten layer 302conformally lines the feature 301. Tungsten growth continues to proceedorthogonally from the feature surfaces, with generally uniform growth asdepicted at stage 360. At stage 370, growth from the sidewall surfacesat pinch point 351 closes off the feature 301, leaving void 312.Returning to FIG. 3A, fill at 310 may be strictly conformal in someimplementations. In some other implementations, the fill may begenerally conformal with some non-conformal aspects. For example,tungsten nucleation may be inhibited at the pinch point 351 to delayclosing the feature 301 off. In either case, a void 312 is present afteroperation 310.

At an operation 320, the feature 301 is opened with an etch that isselective to tungsten. That is, the feature 301 is etched using an etchchemistry that etches tungsten with no significant etch of theunder-layer 313. In the example of FIG. 301, tungsten is etched withoutetching titanium nitride. The etch is allowed to proceed until the pinchpoint 351 is cleared of tungsten. The feature 301 can remain closed offuntil the end of the etch process, keeping the tungsten below the pinchpoint intact. At the same time, the tungsten in the field and at orabove the pinch point is over-etched, thereby exposing the under-layer.Because a selective etch is used, the titanium nitride layer 313 remainson the field region and sidewalls of the pinch point 351. As a result,there is tungsten 303 within the feature 301 below the pinch point 351,with minimal or no tungsten along the sidewalls at and above the pinchpoint 351. If present, any tungsten left is generally insufficient tosupport high quality consistent growth from the sidewalls. For example,it may be discontinuous film in some implementations.

At an operation 330, tungsten is selectively deposited in the feature301 on the remaining tungsten 303. Because tungsten is present onlybelow the pinch point 351, tungsten is deposited selectively below thepinch point 351. The fill in this operation may be characterized asbottom-up.

In some implementations, operation 330 may be performed directly afteroperation 320. The deposition is selective because there is fasterregrowth on the existing tungsten 303 in the feature 301 compared toslow tungsten growth on the exposed under-layer 313 at and above thepinch point 351. In some implementations, tungsten nucleation in thepinch point 351 may be inhibited prior to operation 330. Although notdepicted, in some implementations, operations 320 and 330 may berepeated one or more times. For example, if when performed operation 330results in formation of a seam, an etch may be performed to remove theseam, prior to another selective deposition operation. Removal of a seamis described below with reference to FIG. 3B.

Fill may then be allowed to continue to completely fill the feature 301.In some implementations, the selectively faster regrowth in the featuremay allow for complete fill before the top pinches off (not shown). Insome implementations, the etch and selective fill process can berepeated one or more times to achieve complete fill. If the feature isnot completely filled after one or more iterations of operations 320 and330, in some implementations, an operation 340 may be performed in whicha conformal fill is performed to complete fill of the feature 301.Operation 340 can involve deposition of a tungsten nucleation layer onthe sidewalls of the pinch point 351 in some implementations. In someimplementations, the effects of a previous selective inhibitiontreatment at the pinch point may be diminished at operation 340,allowing conformal fill without deposition of a nucleation layer.

In some implementations, feature fill can involve 1) deposition to filla feature; 2) etch-back to remove tungsten through seam formation; 3)fill by selective deposition; and 4) fill the remainder of the feature.FIG. 3B shows an example of cross-sectional schematic depictions of afeature fill using such a method. First, a feature including a titaniumnitride under-layer 313 is filled using a conformal deposition techniquein an operation 315. In this example, feature 301 has substantiallyvertical sidewalls, with no constriction and so a void does not form inthe feature 301. However, a seam 314 is formed along the axis of thefeature 301 where the growth from each sidewall meets. As growth alsooccurs from the bottom of the feature 301, seam formation starts at apoint 352 above the feature bottom. Deposition is halted at some pointafter seam formation begins; due to the conformal nature of standardCVD-W processes in features, this is generally involves completelyfilling the feature in operation 315 as depicted in the example of FIG.3B. The endpoint may be determined prior to deposition based on thefeature dimensions and tungsten deposition rate. In someimplementations, nucleation inhibition and/or one or more non-conformaletches may be used in operation 315 to tailor the feature profile suchthat the feature is only partially filled at seam formation.

Next, the feature is opened with an etch selective to tungsten, withtitanium nitride (or other under-layer) 313 acting as an etch stop at anoperation 325. The etch is allowed to proceed to at least the point ofseam formation 352, leaving a layer 303 at or below the point of seamformation 352. It should be noted that the etch performed in operation325 may differ in some respects from that performed in operation 320discussed in reference to FIG. 3A. In operation 325, a conformal etch isperformed to remove tungsten uniformly within the feature until thepoint of seam formation is reached. Methods of controlling etchconformality are described further below. In contrast, in operation 320,the etch removes tungsten only near the top of the feature and is morenon-conformal. However, it should be noted that conditions used fornon-conformal etch may not be necessary during operation 320, as thepresence of the closed pinch point 351 prevents etchant diffusion intovoid 312.

Returning to FIG. 3B, the tungsten in the field and above the point ofseam formation is over-etched, thereby exposing the under-layer 313.Because a selective etch is used, the titanium nitride layer 313 remainson the field region and sidewalls of the feature 301. As a result, thereis tungsten 303 within the feature 301 below point of seam formation,with minimal or no tungsten along the sidewalls at and above the pointof seam formation 352.

Next, selective deposition that results in bottom-up fill is thenperformed at an operation 335, with selectivity induced by the fastergrowth kinetics on the tungsten layer 303 in the bottom of the feature.As in the example discussed with reference to FIG. 3A, in someimplementations, selectivity may be further induced be selectiveinhibition of tungsten nucleation in the feature 301 after etchoperation 325 and prior to deposition operation 335. Bottom-up fillmethods using selective inhibition are discussed in U.S. patentapplication Ser. No. 13/774,350, incorporated by reference herein. Insome implementations, operation 335 may be performed until the featureis filled to the top of the feature. In some other implementations,feature fill may be stopped at some point before the top of the featureis reached, particularly if some sidewall growth occurs to form anotherseam. In the example depicted in FIG. 3B, a second etch operation 326 isperformed, after complete or partial fill of the feature 301, to againremove tungsten from the sidewalls. The seam is removed in the etch. Aselective deposition 336 then is performed to fill the feature. Theselective etch and deposition operations may be repeated one or moretimes to fill the feature.

According to various implementations, the methods described above mayalso be used for inside-out fill of horizontally oriented features. Inaddition, while the methods described above with respect to FIGS. 3A and3B use a selective etch that removes tungsten while leaving anunder-layer intact, in some implementations, a barrier layer or otherunder-layer may be removed during etch.

FIG. 4A shows another example of inside-out fill, in which ahorizontally-oriented feature 401 such as a word line (WL) including aconstriction 451 is filled. The feature 401 includes dielectric 419 andtitanium nitride 413 underlayers. (It should be noted that in someimplementations, if image 410 is a side view, constriction 451 mayrepresent a constricted area in the plane extending into the page causedby pillar placement in a 3-D structure, for example.) The top image 410shows the WL fill using standard CVD, wherein a tungsten nucleationlayer is deposited conformally in the feature on titanium nitride layer413 followed by CVD deposition on the tungsten nucleation layer.Tungsten 402 fills the feature with a significant void 412 present inthe WL past the constriction 451. In addition, a seam 414 is present inthe tungsten fill through the constriction 451 to the feature opening401.

In a method as described herein, fill can begin at an operation 420 witha conformal deposition to partially fill the feature, including pinchingoff the void 412. Operation 420 may include conformal tungstennucleation layer deposition on titanium nitride 413 followed by CVDdeposition until the constriction is filled, thereby pinching off thevoid 412. As discussed above, deposition endpoint may be determinedbased on the dimensions of constriction 451 and the tungsten depositionrate.

A conformal etch of tungsten and titanium nitride is performed at anoperation 430 to remove tungsten and titanium nitride deposited betweenthe constriction 451 and the opening of feature 401. In someimplementations, the etch temperature may be relatively high to increaseetch non-selectivity. Dielectric layer 419 may function as an etch stop.The etch may be considered “lateral” or in a direction orthogonal to thefeature axis. The etch can continue at an operation 440 with etchingpast the constriction 451 to remove the tungsten and titanium nitrideuntil the void is removed, leaving only a bottom layer 403 of tungsten.At this point, the etch may be considered “vertical” or in a directionparallel to the feature axis. (It should be noted that the etchconditions do not necessarily change from operation 430 to 440; thedirection of the etch may change due to the thickness and location ofdeposited tungsten to be removed.) The layer 403 can function as abottom tungsten seed layer for subsequent selective deposition. Aselective inside-out fill is then performed at an operation 450.Tungsten is selectively deposited only on the existing tungsten seedlayer 403 and not on the dielectric 419. As with the methods describedabove, in some implementations, etch and selective deposition operationsmay be repeated one or more times. The result is a void-free, seam-freelayer 404 with larger grains and fewer grain boundaries than layer 402shown at 410 filled with conventional CVD. Moreover, TiN under-layer 413is present only at the bottom of the feature. A barrier layer betweentungsten layer 404 and dielectric layer 419 may not be needed; thenon-selective etch of tungsten and titanium nitride can allow more ofthe WL volume to be occupied by tungsten layer 404.

In some implementations, to improve adhesion of inside-out filledtungsten to the substrate, an adhesion layer may be deposited in thefeature or during selective deposition and/or on a field region priorto, during or after inside-out fill of the feature. For example, in FIG.4A, inside-out growth in operation 450 may be halted at some point,followed by deposition of an adhesion layer, with the tungstendeposition then continuing. An example is shown in FIG. 4B, below.

In certain implementations, the methods can include tungsten depositionto fill the feature with suitable overburden thickness. In some cases, adep-etch-dep sequence as described in U.S. patent application Ser. No.13/016,656, referenced above, may be used to achieve void free fill.After the feature is filled, it can be etched at conditions that recesstungsten in the feature, and at the same time remove any under-layer,e.g., one or more of TiN, Ti, WN, or fluorine-free tungsten (FFW) at thefield and along the sidewall up to the recess depth plane. According tovarious implementations, an under-layer dielectric may or may not beremoved. Recess etch can be followed by a bulk tungsten deposition withinside-out (bottom up) growth along the axis of the feature. In someimplementations, if a liner, barrier, or adhesion or other under-layeris removed, another under-layer may be deposited in the field and/oralong the feature sidewall before tungsten deposition in the field andCMP.

Cross-sectional depictions of a feature 401 in an example of a method ofinside-out fill after a recess etch are given in FIG. 4B. First, at 460,a feature 401 is filled with tungsten 402. Feature 401 includesunder-layers 461 and 463, which may be for example any of Ti, TiN, WN,TiAl, etc. A seam 414 is present in the feature 401. At 462, a recessetch is performed to remove tungsten 402, and under-layers 461 and 463to a recess depth plane, leaving an etched tungsten layer 403. Inalternate implementations, under-layer 461 or under-layers 461 and 463may be left with a selective etch. The recess etch removes the seam 414in the recessed volume of the feature 401, which will aid in preventingcoring during a subsequent CMP operation. Accordingly, the recess depthmay be chosen at least in part based on a distance far enough from thefeature opening that the seam 414 will not affect CMP. Methods ofperforming recess etch are described further below. The feature is thenfilled with tungsten in an inside-out fill operation at 464. Atdiscussed above, inside-out fill involves selective deposition on theetched tungsten 403 that remains in the feature 401. This results in aninside-out fill tungsten layer 404 with large, vertically-oriented graingrowth. At 466, the inside-out growth is halted and one or more layers465 are deposited over the feature 401. A layer 465 can be, for example,an adhesion layer or a barrier layer. Examples include Ti, TiN, Ti/TiN,and WN. Depending how well tungsten grows on the exposed surface of theone or more layers 465, a tungsten nucleation layer may then bedeposited on the one or more layers 465. In some implementations, layer465 is a tungsten nucleation layer. An overburden tungsten layer 405 isthen deposited at 468. Though the overburden layer 405 may not bedeposited with bottom-up growth, it will be removed during CMP and somay not present a concern with regard to coring. The feature 401 afterCMP is depicted at 470. In addition to the tungsten layer 404 notpresenting a coring risk during CMP, the large grains of and greatervolume filled by layer 404 provide improved electrical characteristics.

The methods described with reference to FIGS. 2, 2A, 3A, 3B, 4A, and 4Bhave various advantages. For example, while void-free fill can beachieved in most re-entrant features using partial dep-etch-dep cyclesas described in U.S. patent application Ser. No. 13/351,970, referencedabove, depending on the dimensions and geometry multiple dep-etch cyclesmay be needed to achieve void-free fill. This can affect processstability and throughput. Implementations described herein, such as withrespect to FIG. 3A, can provide feature fill of re-entrant features withfewer cycles.

Even if void free fill is achieved, tungsten in the feature may containa seam running through the axis of the via, middle of the trench, orother feature axis. This is because tungsten growth begins at thesidewall and continues until the grains meet with tungsten growing fromthe opposite sidewall. This seam can allow for trapping of impuritieslike hydrofluoric acid (HF), and CMP coring can also propagate from theseam. As shown in FIGS. 3B, 4A, and 4B, the inside-out fill methodsdescribed herein can eliminate or reduce seams. Unlike typical tungstengrowth from the sidewalls, the inside-out fill methods may promotevertical tungsten growth (i.e., growth along the feature's axis) from abottom or interior tungsten seed layer. Thus the formation of a seam canbe avoided, providing advantages such as no trapping of CMP slurry alongthe seam, no trapping of gaseous impurities like HF in the seam, andminimize electron transport losses at the seam in device.

The presence of multiple W grains inside the feature can result inelectron loss due to grain boundary scattering. Actual deviceperformance will be degraded compared to theoretical predictions andblanket wafer results. The methods described with reference to FIGS. 2,2A, 3A, 3B, 4A and 4B can result in fewer grain boundaries, loweringelectrical resistance and improving performance. For example, withreference to FIG. 3B, the grain boundary at seam 314 is eliminated. Insome implementations, vertically oriented grains present in layer 303may continue to grow in subsequent selective deposition operations,reducing the number of grain boundaries.

In cases where the feature sizes are extremely small, tuning the etchprocess without impacting the integrity of the under-layer liner/barriercan be very difficult. In some cases intermittent titaniumattack—possibly due to formation of a passivating TiFx layer during theetch—can occur during a W-selective etch. Accordingly, methods that donot rely on a selective etch, can avoid intermittent titanium attack andthe challenges of selectively etching small features. In certainimplementations, such as the method depicted in FIGS. 4A and 4B,under-layers such as tungsten barrier and liner are removed. As such,the tungsten etch amount does not have to be tightly controlled to avoidcompromising the liner/barrier integrity. This can be useful forextremely small features with very thin tungsten films. For example, inthe case where the liner is titanium, fluorine attack of the titaniumfilm may occur even if the etch process is very selective againsttitanium or titanium nitride etch. By removing the titanium, attack ofthe titanium film by fluorine can be prevented.

Further, if a significant part of the metal contact is used up by thetungsten barrier or other under-layer (TiN, WN, etc.), it may increaseresistance. This is because these films have higher resistivity thantungsten. This may negatively impact electrical characteristics likecontact resistance. For example, in extremely small features like 2× and1×nm contacts, a significant part of the contact can be used up by abarrier material (TiN, WN, etc.) that has a much higher resistivity thantungsten. By etching the barrier and using that volume to grow tungsten,improved electrical performance can be expected.

In certain implementations, the inside-out fill methods can includeimproved process control and repeatability, as they may use conformaletch processes, rather than finely tuned etch processes thatpreferentially etch at feature opening. Under certain processconditions, single grain, seam free, and inside-out tungsten can begrown inside vias, trench-lines, and other features. Further examplesand advantages of inside-out fill methods are discussed below withreference to FIGS. 15, 16, 17, and 19.

According to various implementations, the methods described herein mayinvolve using etches that are selective or non-selective. The methodscan employ methods of tuning etch selectivity such that etchespreferential or non-preferential to W over various under-layers. Forexample, the methods may employ etches that are preferential to W overTiN and Ti, or preferential to TiN and Ti over W, or arenon-preferential.

In some implementations, etching feature fill material includes adownstream (remotely-generated) F-based plasma. FIGS. 5A and 5B showstungsten (W), titanium nitride (TiN) and titanium (Ti) etch rates andW:Ti and W:TiN etch selectivity as a function of temperature at 20 sccmnitrogen trifluoride (NF₃) supplied to remote plasma source. As seen inthe Figures, etch selectivity of W:TiN and W:Ti can be tuned bycontrolling temperature, with the etch becoming preferential to W astemperature decreases. Increasing temperature can also provide etchespreferential to TiN and Ti over W. FIGS. 5C and 5D show the effect oftemperature at 50 sccm. The graphs demonstrate the temperature and flowrate can be adjusted to tune etch selectivity. Further information isdescribed in U.S. patent Ser. No. 13/536,095, filed Jul. 28, 2012 andincorporated herein by reference. As described therein, temperature,etchant flow rates, and other parameters may be controlled to providingW:TiN and W:Ti etch selectivities that ranges from <0.5:1 to >100:1. Forexample, an etch selective to W over TiN may be performed usingremotely-generated fluorine radicals, at temperatures less than 100° C.or 75° C. Similarly, a non-selective etch may be performed at highertemperatures.

Recess Etch and Etch Step Coverage Modulation

In some implementations, the methods described herein provide theability to combine lateral etching with a desired degree of conformalityalong with vertical recess etching in filled features. For some newtechnologies and applications like buried word line (bWL) and onecylinder storage (OCS), only the lower part of the feature may be filledwith tungsten, with the upper part an open volume allowing for fill witha different material. FIG. 6 shows an example of a feature 601 having arecessed tungsten layer 603. Recessed layer 603 is recessed from theopening 602, with the recessed depth D substantially uniform across thefeature 601. Since standard W-CVD is a conformal deposition process andtungsten grows laterally into the feature from the sidewalls, such aprofile is difficult to achieve using a standard W-CVD process. Openvolume 605 is available to be filled with another material in someimplementations. In addition to bWL and OCS applications in which onlythe lower part of the feature is filled with tungsten, a recessedtungsten layer may be used as a seed for inside-out fill in a feature.An example is discussed above with respect to FIG. 4B.

In cases like 3-D NAND and vertical integrated memory (VIM) devices,tungsten fill is expected at and beyond pinch point locations. In suchapplications, lateral tungsten growth, e.g., due to reaction between WF₆and H₂ molecules or other reactants, at the pinch point locationprevents diffusion of WF₆ and H₂ to the wider regions beyond the pinchpoint resulting in voiding. The methods provided here can overcome suchvoiding. In some implementations, one or both of two approaches can beused together or separately. One approach involves allowing a void toform and then vertically etching through with a etch process that may ormay not have selectivity against the under-layer, opening up the voidand re-filling with tungsten. The other approach involves partialtungsten deposition followed by carefully tuning the etch conditions toachieve the desired degree of etch conformality such that more tungstenis etched at the pinch point compared to beyond the pinch point. Someexamples of potential incoming profiles and resulting tungsten fill areshown in FIG. 1C. Either or both approaches may be used together withthe inside-out fill methods described above with respect to FIGS. 2-4B.For example, FIGS. 3A and 4A depict methods in which a void is opened upand the feature re-filled with tungsten. In another example, FIGS. 3Band 4B depict initial void-free conformal fills that may use partialdep-etch-dep approaches. Moreover, selective deposition in any of theinside-out fill methods may involve dep-etch-dep techniques in whichetch conformality is tuned to shape the inside-out tungsten growth.Recessing may progress vertically (along the feature axis) or laterally(orthogonal to the feature axis, toward the sidewalls) in the featuredepending on existing voids, grain positioning and feature geometry.

As mentioned above, W-CVD growth is in the lateral direction from thesidewalls. To achieve a final profile as illustrated in FIG. 6, in someimplementations, the structure is filled structure completely with W-CVDfollowed by a vertical etch to create the recess or open volume. In someimplementations, the etch conditions can be selective to etch only W andavoid etching the under-layer material. FIG. 7 shows a feature 701filled with tungsten 702 using a standard CVD-W process, for example. Arecess etch is performed to form recessed tungsten layer 703 and openvolume 705. The open volume 705 can be filled by WN or other material,for example. In some implementations, the recess etch may be performedin one, two, or more etch operations. For example, in a first operation,a fast process to remove tungsten in the field region 720, followed by amore finely controlled process to etch in region 722 and control therecess depth. In one example, the faster process could be performedusing a higher temperature, higher etchant flow rate and, for aplasma-based etch, a higher plasma power. Example etch rates may bebetween 10 Å/sec-50 Å/sec for a faster etch. A slower, more controlledprocess may be done using lower etchant flow and, for a plasma-basedetch, lower plasma power. Depending on desired etch selectivity withrespect to an under-layer, the temperature may or may not be lowerduring the controlled etch than during the faster etch. Example etchrates may be between 3 Å/sec-20 Å/sec or 3 3 Å/sec-10 Å/sec for acontrolled etch.

In some implementations, similar recess etching can be useful to achievefill in structures like those shown in FIG. 1C. For the simplest of thecases in panel (a) of FIG. 1C, the constriction 109 will cause severevoiding in the lower part 119 of the feature. In some implementations,overcoming such voiding involves etch back till the void is opened upallowing for re-filling the void with W-CVD. In certain cases, due tothe feature dimensions, the etch back may be lateral (toward thesidewalls) for the top part 121 of the structure and vertical (in thedirection of the feature axis) in the constriction 109. In someimplementations, multiple dep-etch cycles may be used to achievecomplete fill throughout. FIG. 8 illustrates one potential sequence.

FIG. 8 shows a sequence in which a feature 801 including a constriction851 is filled. It should be noted that feature 801 may be ahorizontally-oriented feature (such as word line feature 401 in FIG. 4A)or a vertically-oriented feature. The feature 801 includes under-layers813 and 819. At 810, feature fill using standard CVD-W is shown. Notethat this similar to fill of feature 401 using standard CVD-W shown inFIG. 4B; tungsten 802 fills the feature with a significant void 812present in the feature 801 past the constriction 851.

In a method as described herein, fill can begin at an operation 820 witha conformal deposition to partially fill the feature, including pinchingoff the void 812. Operation 820 may include conformal tungstennucleation layer deposition on under-layer 813 followed by CVDdeposition until the constriction 851 is filled, thereby pinching offthe void 812. As discussed above, a deposition endpoint may bedetermined based on the dimensions of constriction 851 and the tungstendeposition rate. At this stage, the method is similar to that describedin FIG. 4A. Next, an etch of tungsten is performed at an operation 830to remove tungsten deposited between the constriction 851 and theopening of feature 801. Unlike the method depicted in the example ofFIG. 4A, the etch in this example is selective to tungsten over theunder-layer 813, such that the under-layer 813 acts as an etch stop. Insome implementations, the etch performed at 830 is a recess etch asdescribed above, with the recess depth indicated at 849. The etch cancontinue at an operation 840 with etching past the constriction 851 toremove the tungsten in the lower part 852 of the feature until the voidis re-opened. In some implementations, the feature dimensions, includingthe remaining tungsten layer 803, are such that subsequent conformalfill may be performed without forming a void in an operation 850. If,for example, the dimensions are such that the constriction 851 isapproximately the same or wider than the narrowest dimension in thelower part 852 of feature 801, subsequent conformal deposition may beused for void free fill.

In some implementations, tungsten is completely removed from theconstriction 851, without subsequent deposition of a nucleation layer,in operation 840, to further facilitate void free fill of the lower part852 of the feature in a subsequent operation. In this case, the tungstenmay selectively deposit on the remaining tungsten 803 in the lower partof the feature. Unlike operation 450 in FIG. 4B, the selectivedeposition in the lower part 852 of the feature may result in conformalfill in the lower part 852 of the feature. Selective inhibition oftungsten nucleation in the constriction and, in some implementations, inthe upper part 854 of the feature, may be performed to facilitateselective deposition in the lower part 852 of the feature.

In some implementations, after operation 840, one or more additionaldep-etch cycles may be performed for fill improvement. If performed, oneor more additional dep-etch cycles can involve repeating operations820-840 one or more times. In some other implementations, non-conformaletches may be performed as described further below to tailor the featureprofile for subsequent deposition.

In the example of FIG. 8, at 850, a conformal deposition is performed tocomplete void-free feature fill. This may involve conformal depositionof a tungsten nucleation layer followed by CVD deposition of a tungstenbulk layer, and as discussed above, may be performed directly after oneiteration of operations 820-840 or after one or more additional etch andor deposition operations.

In more complicated geometries, the profile of the top portion may bere-entrant like examples shown in panels (b) and (c) of FIG. 1C. Due tovarious reasons, the re-entrant section may be near the surface/field(see, e.g., overhang 115 in panel (b)) or deeper inside the feature(see, e.g., constriction 112 in panel (c)). In such cases, the samesequence as shown in FIG. 8 could be followed up to the penultimatestep. A non-conformal etch can then be performed to preferentially etchat the pinched-off section only, with minimal or no etching below.

Aspects of non-conformal etching are described in U.S. patentapplication Ser. No. 13/351,970, incorporated by reference herein, wherea via is partially filled with tungsten, followed by fluorine based etchof tungsten to etch more tungsten near the opening than further in thefeature. This may be followed by tungsten deposition to fill thefeature. (It should be noted non-conformal etching in U.S. patentapplication Ser. No. 13/351,970 is referred in places as “selectiveremoval,” due to the fact that more material is removed at certainlocations of a feature than at other locations. Selective removal asdescribed therein is distinguished from selective etch of one materialover another described above.) Non-conformal etching can also bereferred to as preferential or low-step coverage etch. To obtain thepreferential (or low step coverage) etch, the etch process conditionsare carefully designed. A combination of the right etch temperature,etchant flow and etch pressure can help to achieve the desiredconformality. If the etch conformality is not tuned right for each typeof re-entrant structure, this could result in poor fill even after thedep-etch-dep sequence.

Step coverage is proportional to (reactant species available forreaction)/(reaction rate). For some implementations of feature etchdescribed herein in which the principle etchant is atomic fluorine, thiscan be simplified to:

${W\mspace{14mu} {step}\mspace{14mu} {coverage}} \propto \frac{\left( {{atomic}\mspace{14mu} F\mspace{14mu} {concentration}} \right)}{{etch}\mspace{14mu} {rate}}$

Accordingly, to achieve a certain tungsten etch step coverage (ordesired etch conformality or etch non-conformality), the NF₃ flow rate(or other F-containing flow rate) and etch temperature are keyparameters since they directly affect the concentration of atomicfluorine and etch rate. Other variables like etch pressure and carriergas flows also carry some significance.

At higher temperatures, the incoming fluorine atoms readily react andetch at the feature entrance, resulting in a more non-conformal etch; atlower temperature, the incoming fluorine atoms are able to diffuse andetch further into the feature, resulting in a more conformal etch.Higher etchant flow rate will result in more fluorine atoms generated,causing more fluorine atoms to diffuse and etch further into thefeature, resulting in a more conformal etch. Lower etchant flow ratewill result in fewer fluorine atoms generated, which will tend to reactand etch at the feature entrance, resulting in a more non conformaletch. Higher pressure will cause more recombination of fluorine radicalsto form molecular fluorine. Molecular fluorine has a lower stickingcoefficient than fluorine radicals and so diffuses more readily into thefeature before etching tungsten, leading to a more conformal etch. FIG.9A shows cross-sectional schematic illustrations of partial depositionand etch in features 901 and 902 that have different profiles. Feature901 includes a constriction 951 mid-way down the feature; while feature902 includes an overhang 915 near the feature opening. Standard CVD-Wwould result in voids within the feature due to pinch-off byconstriction 951 and overhang 915, respectively. The etch of feature 901is a more conformal etch at lower temperature and/or more etchantspecies, in this example fluorine radicals (F*), to allow the etchantspecies to diffuse further into the feature. The etch of feature 902 isa more non-conformal etch at higher temperature and/or less etchantconcentration.

FIG. 9B is a plot of the etch rate as a function of etch temperature fordifferent NF₃ flows. Etch conformality can be increased by devising alow etch rate process with high NF₃ flow rates. In one example, theregion marked “highly selective and high conformal etch” shows processconditions at which the etch is selective (to W over Ti or TiN) andhighly conformal throughout the feature. While the lowest etchtemperature and highest NF₃ flows tested were 25° C. and 100 sccmrespectively, even higher conformality can be achieved by reducing theetch temperature and increasing NF₃ flow (more atomic F radicals) toachieve a reaction rate limited regime. Conversely, etchnon-conformality can be increased by working in a mass transport limitedregime wherein high etch rates are achieved with low NF₃ flows (feweratomic F radicals). See, for example, the region marked “mildlyselective and highly non-conformal etch.” Further discussion of workingin mass transport limited and reaction rate limited regimes is providedbelow.

In some implementations, conformal etching may involve one or more ofthe following process conditions: temperature below about 25° C.,etchant flow above about 50 sccm, and pressure greater than about 0.5Torr. In some implementations, non-conformal etching may involve one ofthe following process conditions: temperature above about 25° C.,etchant flow below about 50 sccm, and pressure greater less about 2Torr. A desired level of step coverage (e.g., 60% step coverage) mayinvolve adjusting one or more of these process conditions to make theprocess more or less conformal.

Depending on the location of the pinch off in a feature, the etchprocess can be tailored to achieve a desired etch step coverage. Thenon-conformal etch process can be added to the sequence of FIG. 8 asshown in FIG. 10, discussed further below. Buried word line, onecylinder storage, VNAND and other 3D devices are applications wheretraditional W fill process may not be sufficient, and where the methodsdescribed herein can achieve a desired tungsten profile. Further, theability to tailor the etch step coverage by adjusting process conditionsis useful achieve good fill in different profiles. In radical-basedetches, the low temperature etch regime minimizes the contribution ofrecombined species (e.g., F₂ species) and with the flow control enablesradicals (e.g., F radicals) to be used both for non-conformal andconformal etch conditions. The radical-only etch is also more surfacelimited in that the radicals would be less likely to diffuse through andopen up small seams, or penetrate pinholes as compared to recombinedspecies. This enables a series of new approaches to etch: instead ofrelying on partial fill, a seam can be closed, with the overburdenetched back for example. In another example, the top layer of tungstenin a buried word line (bWL) can be etched without reopening the seam.The methods can provide different types of etch capabilities atdifferent process conditions for various operations.

While etch conformality modulation is describe above chiefly in thecontext of radical-based etches, etch conformality may also be modulatedusing other types of etches. For example, temperature, pressure, flowrate, and etchant species may be used to control non-plasma chemicaletches. These parameters and any bias applied to the substrate may beused to control ionic-based etches. In one example, a higher power biasmay be used to etch further within a vertically-oriented feature.

In some implementations, a non-conformal etch may be used to shape atungsten profile prior to deposition at various stages in the methodsdescribed above with respect to FIGS. 2-8. FIG. 10 is an example of onemethod in which a non-conformal etch may be used in deposition in anupper part 1054 of a feature 1001 after void-free fill is achieved inthe lower part 1052 of the feature 1001. At 1010, feature 1001 includingconstriction region 1051, upper part 1054 above the constriction region1051, and lower part 1052 below the constriction region 1051, isdepicted after tungsten fill following lateral and vertical etch cycles.The lower part 1052 of the feature 1001 below constriction region 1051is void-free and filled with tungsten, e.g., using a process asdescribed in FIG. 8. However, a void 1012 is present in the upper part1054 due to the presence of constriction 1053.

In some implementations, rather than fill the feature 1001 as depictedat 1010, fill can first involve partial fill performed at an operation1020 with deposition halted before the area of upper part 1054 belowconstriction 1053 is pinched off. Void-free fill in lower part 1052 canbe accomplished by any of the methods described above. The upper part1054 is partially filled with tungsten in a conformal depositionprocess. A non-conformal etch is then performed at 1030 to etch only atand above constriction 1053, eliminating the re-entrant profile. Aconformal deposition 1040 can then be used to complete void-free featurefill.

Accordingly, one possible sequence to fill a feature having twoconstrictions at different feature depths may be: (1) tungstennucleation+CVD bulk deposition until pinch off at lower constriction andvoid formation below lower constriction (see, e.g., operation 820 ofFIG. 8), (2) conformal etch to remove all tungsten above and throughlower constriction and re-open void (see, e.g., operations 830-840 ofFIG. 8), (3) tungsten nucleation+CVD bulk deposition for void free fillbelow and at lower constriction and partial fill above lowerconstriction (see, e.g., operation 1020 of FIG. 10), (4) non-conformaletch above lower constriction to shape tungsten profile above lowerconstriction (see, e.g., operation 1030 of FIG. 10), and (5) conformaldeposition to complete void free feature fill (see, e.g., operation 1040of FIG. 10). The sequence described is an example of how etchconformality modulation may be used at different times during featurefill to achieve void-free fill, with other sequences possible dependingon the feature profile. In addition to etch conformality modulation,selective deposition and conformal deposition may also be used atdifferent times during feature fill to control deposition profiles andachieve void free fill.

Also as described above, in some implementations, selective passivationof a feature may be employed to control feature fill. Selectivepassivation is described, for example, in U.S. patent application Ser.Nos. 13/351,970 and 13/774,350, both of which are incorporated byreference herein, and further below, with reference to FIGS. 11 and 12.

Feature Fill with Boron Conversion

In some implementations, feature fill can include conformal borondeposition, followed by reduction of a tungsten-containing precursor(such as WF₆) by boron to form a layer of tungsten. An example reactionis:

WF₆(g)+2B(s)→W(s)+BF₃(g)

FIG. 13A shows a flow diagram illustrating certain operations in such amethod of filling a feature. First, in an operation 1310, a thinconformal layer of boron 1325 is deposited in a feature 1301 over atitanium nitride layer 1313. In an operation 1320, the thin conformallayer of boron 1325 is converted to a tungsten layer 1327, for example,by the reaction given above. The boron deposition and conversionoperations are repeated at 1330 and 1340 to form another conformal layerof boron 1325 that is then converted to tungsten, such that tungstenlayer 1327 grows. The deposition and conversion reactions can berepeated until the feature is completely filled with tungsten 1327. Theuse of multiple cycles of thin conformal boron (or another reducingmaterial) and conversion to tungsten to deposit very conformal, smallgrain and smoother tungsten can reduce the seam that may otherwise formusing a CVD method that results in large or uneven grain growth. In someimplementations, each cycle may form a tungsten layer having a thicknessup to about 10 nm. There may be an increase in volume associated withthe conversion from boron to tungsten.

Any boron-containing compound that can decompose or react to form alayer capable of reducing the tungsten-containing precursor to formelemental tungsten may be used in operation 1310 and subsequent borondeposition operations. Examples include boranes including B_(n)H_(n+4),B_(n)H_(n+6), B_(n)H_(n+8), B_(n)H_(m), where n is an integer from 1 to10, and m is a different integer than m. Other boron-containingcompounds may also be used, e.g., alkyl boranes, alkyl boron,aminoboranes (CH₃)₂NB(CH₂)₂, carboranes such as C₂B_(n)H_(n+2), andborane halides such as B₂F₄.

In some implementations, layer 1325 may be any material that is capableof reducing a tungsten precursor including a silicon orsilicon-containing material, phosphorous or a phosphorous-containingmaterial, germanium or a germanium-containing material, and hydrogen.Example precursors that can be used to form such layers include SiH₄,Si₂H₆, PH₃, SiH₂Cl₂, and GeH₄. Another example of using boron conversionin tungsten feature fill is described below with reference to FIG. 18.

The method described with reference to FIG. 13A differs fromconventional ALD processes that use diborane or other reducing agents.This is because the deposited conformal boron (or other reducing agentlayers) and resulting tungsten layers are significantly thicker thandeposited in conventional ALD methods. For example, example thicknessesfor each boron layer 1325 may range from about 1.5 nm to 10 nm, or insome implementations, 3 nm to 10 nm, or 5 nm to 10 nm.

The upper limit of thickness may be determined by the maximum thicknessthat can be converted to tungsten at various process conditions. Forconversion at 300° C. to 400° C. and 40 Torr using WF₆, a limit of about10 nm was found. The maximum thickness can vary depending on thetemperature, pressure, solid reducing agents, and tungsten precursors.For example, using a higher pressure and/or temperature may allow areducing agent layer up to 100 nm to be converted. In someimplementations, the thickness of each boron (or other reducing agent)layer may between about 5 nm to 50 nm or 10 nm to 50 nm.

In some implementations, the volumetric expansion that takes place onconversion to tungsten is particularly helpful for fill. For example,each layer that is converted to tungsten from a reducing agent may be upabout 5% thicker than the reducing agent layer.

In some implementations, tungsten fill may be performed using boron asan etch stop. The conversion to tungsten may be limited in someimplementations to about 10 nm, which can allow partial conversion totungsten, followed by an etch selective to tungsten over boron to tailorfeature fill. FIG. 13B is a flow diagram illustrating operations in anexample of a method in which a boron layer is partially converted totungsten and used as an etch stop. The method begins with conformalboron deposition in a feature (1352). According to variousimplementations, conformal boron deposition may occur prior to or afterinitial tungsten deposition in the feature. In various implementations,for example, the boron is formed on a barrier or liner layer surface, atungsten surface, or a combination of these surfaces. Block 1352 caninvolve exposing the feature to a boron-containing compound. In someimplementations, the boron-containing compound undergoes thermaldecomposition to form elemental boron (B) or a boron-containing layer onthe feature surface. The boron layer may also be deposited by a suitablechemical reaction. Example boron-containing compounds are given above.

If thermal decomposition is used to deposit boron (or other conformalmaterial), then temperature in block 1352 is higher than thedecomposition point. For B₂H₆, for example, the temperature is greaterthan 250° C. B₂H₆ has been successfully used with 450 sccm flow at 300°C., 375° C., and 395° C. and 40 Torr for conformal boron deposition, asexamples, though flow rates, temperatures, and pressures different fromthese may also be used. Block 1352 can involve continuous flow orpulsing the boron-containing compound for until the desired thickness ofboron is formed.

Next, the deposited boron is partially converted to tungsten, leaving aportion of the boron-film remaining. (1304). Block 1304 generallyinvolves exposing the boron layer to a tungsten-containing precursorvapor with which it will react to leave elemental tungsten. An exampleof a reaction between tungsten hexafluoride gas and solid boron is givenabove. The temperature is such that a spontaneous reaction will takeplace. For example, tungsten hexafluoride has been successfully used forconversion to tungsten with a flow rate of 400 sccm at 40 Torr, at 300°C. and 395° C., for example. The amount of boron converted can depend onthe flow rate, pressure, temperature and duration of flow of thetungsten-containing precursor. However, the conversion to tungsten maybe limited to about 10 nm. Accordingly, in some implementations, if morethan 10 nm of boron is formed in block 1352, only about up to the top 10nm of boron is converted to tungsten, leaving a boron-tungsten bilayer.

Next, tungsten is selectively etched with respect to boron (1306). Insome implementations, the boron acts as an etch stop. In this manner,the feature fill may be tailored. For example, the boron layer may beused similarly to the under-layers shown in FIGS. 3A, 3B, 8 and 10 thatact as etch stops in feature fill. Unlike those under-layers, in someimplementations, the remaining boron may be converted to tungsten afterthe etch process (1308). In this manner, more of the feature is occupiedby a lower resistivity material. In some implementations, boron isformed in block 1302 to a thickness of no more than about 20 nm suchthat it can all be converted to tungsten in two conversion operationsthat each convert up to about a 10 nm thick layer of boron to tungsten.Similarly, in some other implementations, boron may be formed to athickness of no more than n×10 nm, wherein n is the number of etchoperations to be performed. An example of a process as described withreference to FIG. 13B is discussed below with reference to FIG. 19.

Controlling etch selectivity to use boron as an etch stop may involveadjusting temperature, flow rates, and other parameters, e.g., asdescribed above with respect to W:Ti and W:TiN etch selectivities. Inone example, boron acts as an etch stop using a 25° C. F-based remoteplasma etch using NF₃→NF_(x)+F* chemistry. At these temperatures, the Wselectively etches faster than the B, which may be related to thethermodynamics of the reactions B+3F*→BF₃ vs. W+6F*→WF₆. Other types ofetches and etch chemistries may be modu

The method described in FIG. 13B may also be used with other solidlayers instead of or in addition to boron. For example, silicon orsilicon-containing material, phosphorous or a phosphorous-containingmaterial, germanium or a germanium-containing material may be depositedand partial converted to tungsten via a reaction with atungsten-containing precursor as described above with respect to FIG.13A. It should be noted that while a conversion limit of about 10 nm hasbeen observed for WF₆ using particular process conditions, conversionlimits may be experimentally or theoretically determined for othertungsten-containing compounds and/or other reducing agents. Accordingly,the methods described herein may be adjusted to deposit more or lessreducing agent prior to partial conversion of the reducing agent totungsten.

Feature Fill with Fluorine-Free Tungsten (FFW) and Tungsten Nitride(FFWN)

FIGS. 13C and 13D are flow diagrams showing certain operations inexamples of using fluorine-free layers in feature fill. Fluorine (F) intungsten and tungsten precursors may react during further integrationoperations to form highly reactive hydrofluoric acid (HF). HF can eatinto oxide in oxide stacks, for example, or otherwise negatively affectintegration.

FIG. 13C shows one example in which a fluorine-free tungsten nitridelayer can be deposited in a feature, then converted to a fluorine-freetungsten layer. First, a fluorine-free tungsten nitride layer isdeposited in a feature (1352). In some implementations, the tungstennitride layer is deposited by a thermal ALD or PNL process in which areducing agent, tungsten-containing precursor, and nitrogen-containingreactant are pulsed (in various orders) to form a conformal tungstennitride layer on the feature. Examples of ALD and PNL processes todeposit tungsten nitride films are described in U.S. Pat. No. 7,005,372and U.S. Provisional Patent Application No. 61/676,123, both of whichare incorporated by reference herein.

To deposit fluorine-free layers, generally all of the reactants arefluorine-free. In some implementations, the nitrogen-containing compoundacts as the reducing agent, such that a separate reducing agent may ormay not be used. In some implementations, the tungsten-containingprecursor may also include nitrogen, such that a separatenitrogen-containing compound may or may not be used.

Examples of fluorine-free tungsten precursors that may be used includeW(CO)₆ and organotungsten precursors such as W₂(NMe₂)6, W(OEt)₆,W(OnPr)₆, (tBuN=)₂W(NMe₂)₂, (tBuN=)₂W(NEtMe)₂W(Cp)₂H₂, W(NEt₂)₂(NEt)₂,W(iPrCp)₂H₂, (tBuN=)₂W(HNMe)₂, W(EtCp)₂H₂ and derivatives thereof.Further examples includeethylcyclopentadienyl-dicarbonylnitrosyl-tungsten (EDNOW),methylcyclopentadienyl-dicarbonylnitrosyl-tungsten (MDNOW), andethylcyclopentadienyl)tricarbonylhydridotungsten (ETHW), available fromPraxair, as well as tungsten bis(alkylimino)bis(alkylamino) compoundshaving the following structure:

where each R may be independently selected from methyl, ethyl, propyl,butyl and tert-butyl groups. These groups may be substituted orunsubstituted, though are typically unsubstituted. For example, thetungsten-containing precursor is bis(tert-butylimino) bis(dimethylamino)tungsten (W[N(C₄H₉)]₂[N(CH₃)₂]₂.

Examples of reducing agents include boranes, silanes, H_(z), NH₃, N₂H₄,and combinations thereof. Examples of nitrogen-containing compoundsinclude N₂, NH₃, N₂H₄, and N₂H₆. In some implementations, the depositedfilm is a WN film having relatively little carbon, e.g., less than about5 atomic % or less than about 2 atomic % carbon. In someimplementations, a CVD method of depositing tungsten nitride may beemployed in block 1352 in addition to or instead of an ALD or PNLmethod. In one example, thermal ALD using an organo-tungsten precursoror W(CO)₆ can be used to deposit a WN layer, without pinching off afeature in block 1352.

In various implementations, the as-deposited W content in the FFWN filmmay range from about 20% to 80% (atomic) with the N content ranging fromabout 10% to 60% atomic. Some amount of carbon may be present asindicated above. Moreover, as discussed below with respect to tungstenfilms, other elements may be present including oxygen, boron,phosphorous, sulfur, silicon, germanium and the like, depending on theparticular precursors and processes used. Above-referenced U.S.Provisional Patent Application No. 61/676,123 discusses deposition ofternary WBN films, for example.

Returning to FIG. 13C, the fluorine-free tungsten nitride is thenconverted to fluorine-free tungsten (1354). This is generally done bythermally annealing the tungsten nitride at temperatures of at leastabout 600° C. for a period of time, e.g., between about 5 seconds and120 seconds, such that the nitrogen in the tungsten nitride film leavesas nitrogen gas (N₂). In some implementations, block 1352 is performedwithout closing off the feature to allow a flow path for the volatilizedN₂ gas. For example, leaving at least about 1 to 2 nm open at a pinchpoint or constriction may allow the anneal to convert substantially allof the tungsten nitride to tungsten.

Once the tungsten nitride film is converted to tungsten, a furtherfluorine-free tungsten or tungsten nitride film may optionally bedeposited to close off any constrictions and/or complete feature fill(1358). Deposition of a fluorine-free tungsten nitride film is describedabove with respect to block 1352. Deposition of a fluorine-free tungstenfilm may be performed using a thermal ALD or PNL process in which areducing agent and fluorine-free tungsten-containing precursor arepulsed to form a conformal tungsten layer on the feature. According tovarious implementations, one or more other techniques described herein,including inside-out fill, recess etch, etch conformality modulation,and boron conversion may be used to complete void-free feature fill insome implementations, while using fluorine-free precursors and reducingagents. In some other implementations, a feature may be capped with afluorine-free WN or W layer, while leaving a void within the feature.The cap layer may be employed to close off the gas flow pathway left inblock 1352. If a fluorine free tungsten nitride layer is deposited inblock 1358, it may or may not be followed by a thermal anneal to convertit to elemental tungsten. In some implementations, for example, it maynot be particularly advantageous to convert a thin WN layer (e.g, 5 Å)to W. An example of a process according to FIG. 13C is described belowwith reference to FIG. 22.

FIG. 13C is a flow diagram illustrating certain operations in an exampleof a method which a fluorine-free tungsten-containing layer may be usedto seal a tungsten layer deposited using a fluorine-containing gas.First, a feature is partially filled with a tungsten layer depositedwith a fluorine-containing compound (1362). Block 1362 can involvedepositing a tungsten nucleation layer followed by a depositing a bulktungsten layer using a precursor such as tungsten hexafluoride. Partialfill is performed, keeping the feature open. This allows HF gas to bepumped out of the feature in block 1364 and, in some implementations,may allow a fluorine-free layer to be deposited on the layer in block1368.

Next, any HF (or other fluorine-containing gas) generated as a reactionbyproduct or otherwise present in the feature is pumped out (1364). Insome implementations, some fluorine may be present in the remainingtungsten film. The tungsten film can be sealed using a HF-free process,for example depositing a fluorine-free tungsten or tungsten nitridelayer as described above or using a boron conversion with a fluorinefree tungsten precursor. According to various implementations, anyconstrictions may be sealed with a fluorine-free film and/or any exposedsurface of tungsten film deposited in block 1362 may be covered with afluorine-free film. This can prevent any fluorine that may be present inthe film from forming hydrofluoric acid during integration. The methoddescribed with respect to FIG. 13D may be useful to efficiently depositmost of the tungsten in the feature with a fluorine-based process, whileallowing preventing any remaining fluorine from affecting subsequentintegration.

According to various implementations, the film deposited in block 1368may close off any constrictions and/or complete feature fill. Accordingto various implementations, one or more other techniques describedherein, including inside-out fill, recess etch, etch conformalitymodulation, and boron conversion may be used to complete void-freefeature fill in some implementations, while using fluorine-freeprecursors and reducing agents.

While the methods described above with reference to FIGS. 13C and 13Drefer to fluorine-free tungsten and tungsten nitride, they may begeneralized to halogen-free tungsten and tungsten nitride films.Similarly, the tungsten deposited in block 1362 may be deposited with ahalogen-containing precursor such as WCl₆.

Feature Fill Examples

Aspects of the invention will now be described in the context of VNANDword line (WL) fill. While the below discussion provides a framework forvarious methods, the methods are not so limited and can be implementedin other applications as well, logic and memory contact fill, DRAMburied word line fill, vertically integrated memory gate/word line fill,and 3-D integration with through-silicon vias (TSVs). The processesdescribed below may be applied to any horizontally orvertically-oriented structure including one or more constrictions,including tungsten via and trench fill.

FIG. 1F, described above, provides an example of a VNAND word linestructure to be filled. As discussed above, feature fill of thesestructures can present several challenges including constrictionspresented by pillar placement. In addition, a high feature density cancause a loading effect such that reactants are used up prior to completefill. Various methods are described below for void-free fill through theentire WL. In certain implementations, low resistivity tungsten isdeposited. Also in certain implementations, the film has a low F contentwith no HF trapping. In some implementations, the feature may not becompletely filled, with feature fill halted prior to the fill reachingthe feature opening. An example is shown in FIG. 17 at 1740.

FIG. 14 shows a sequence in which conformal deposition operations arealternated with an etch with a high W:TiN etch selectivity in a feature.The feature 1401 includes constrictions 1451, and an interior region1452 that may be accessible from two ends 1455. As discussed above withrespect to FIG. 1G, FIG. 14 can be seen as a 2-D rendering of a 3-Dfeature, with the figure showing a cross-sectional depiction of an areato be filled and the constrictions 1451 representing constrictions frompillars that would be seen in a plan rather than cross-sectional view.FIGS. 1E and 1F above provide additional description of how pillars maybe arranged. The feature includes an under-layer 1413, which in theexample of FIG. 14 is a TiN layer, though it may be any under-layer. Thesequence begins at 1410 with conformal deposition of tungsten to fillthe feature, leaving a void 1412 in the interior of the feature.

An etch selective to W over the under-layer TiN is then performed at1420 to leave tungsten 1403 within the feature, as described above withreference to FIG. 2, 7 or 8, for example. The remaining tungsten 1403provides feature dimensions in the feature interior 1455 that are closerto the dimensions at the constrictions 1451. This allows void formationin subsequent conformal deposition to be reduced or eliminated. Forexample, in another conformal deposition at 1430, two voids 1414 areformed that are smaller and closer to the feature ends 1455 than void1412 formed at 1410. A selective etch performed at 1440 can open voids1414, re-shaping the feature profile so there is no re-entrancy in thefeature. A final conformal deposition at 1450 can provide void free fillof the word line. It should be noted that in the depicted example, thedeposition operations are conformal, and may involve deposition of aconformal nucleation layer in the feature. The exact profiles of theresidual W left after etching can vary according to the particularimplementation.

FIG. 15 shows a sequence similar to FIG. 14, but with selective ratherthan conformal depositions to provide inside-out fill as discussed abovewith reference to FIGS. 3A-4B, for example. The process begins at 1510with a conformal deposition, e.g., a PNL nucleation layer plus CVDoperation, to pinch off the feature. Next, an etch selective to W isperformed at 1520 to open the constrictions, leaving an etched tungstenlayer 1503. Selective deposition (typically with no new conformalnucleation layer) of tungsten is then performed to achieve inside-outfill and pass the constrictions. The progression of a CVD operation usedto fill the interior region 1555 of the feature and then passconstrictions 1551 is shown at 1530 and 1540, respectively. In thedepicted example, a conformal deposition can be used to complete fill at1550. The conformal deposition can involve deposition of a tungstennucleation layer in the unfilled end portions of the feature, followedby bulk deposition. In some implementations, the initial deposition andetch operations 1510 and 1520 in FIG. 15 may result in profiles similarto those in operations 1410 and 1420 FIG. 14 (and vice-versa). Also insome implementations, the depositions to finish fill at 1450 and/or 1550can involve one or more of selective removal operations and/orpassivation operations as described above.

FIG. 16 shows a variation on inside out growth process shown in FIG. 15.Similar to operation 1510 in FIG. 15, the process begins at 1610 with aconformal deposition, e.g., a PNL nucleation layer plus CVD operation,to pinch off the feature. Next, an etch selective to W is performed at1620 to open the constrictions, leaving an etched tungsten layer 1603.Selective deposition (typically with no new conformal nucleation layer)of tungsten is then performed at 1630 to achieve inside-out fill andpass the constrictions. The profile of the etched tungsten layer 1603differs from that formed at 1520 in FIG. 15, which may affect theprogression of the selective deposition. In both examples, however, theetched tungsten layer acts as a seed layer for subsequent CVD andfacilitates inside-out fill. A conformal deposition can be used tocomplete fill at 1640. This can involve one or more of selective removaloperations and/or passivation operations as described above in someimplementations.

FIG. 17 shows a sequence using a selective and non-selective W/TiNetches. A film is first deposited conformally in a feature at 1710leaving a void 1712. An initial selective etch can be used to etch intothe pinch point at 1720, followed by an etch that is non-selective to Wand TiN at 1730. The remaining film can be used as a seed layer forselective deposition of W at 1740.

FIG. 18 shows a sequence in which a boron layer is converted totungsten. The method can start by allowing boron to adsorb onto thesubstrate, e.g., using diborane or other boron-containing precursor at1810. The thickness can be near the pinch off point, e.g., 10 nm thick.As noted above, in some implementations, 10 nm may be approaching thelimit for tungsten conversion in a reasonable amount of time. Tungstenhexafluoride or other tungsten-containing precursor can then be reducedby the boron layer, to form elemental tungsten at 1820. There may athickness expansion associated with the conversion (3.6% based on atomicvolume.) According to various implementations, the conversion may or maynot seal off the feature below the constrictions. In someimplementations, no hydrogen is used during the conversion, such that noHF is trapped within the feature. The F concentration within theboron-converted tungsten is low. According to various implementations,the feature may be filled with tungsten without forming a tungstennucleation layer. Also in some implementations, the boron deposition andconversion operations may be repeated, e.g., as shown in FIG. 13A. Stillfurther, in some implementations, tungsten conversion may be followed byone or more conformal or selective tungsten deposition operations, ordeposition-etch-deposition operations, to complete feature fill.

FIG. 19 shows another sequence involving boron conversion to tungsten.In the depicted example, boron is alternately used as an etch stop foretch tungsten and converted to tungsten. The tungsten can be etched toleave a starting layer for inside-out fill. One or more conformal orselective depositions or combinations thereof can be used to completethe fill. Because the conversion may be self-limiting to about 10 nm,boron deeper into the feature is left unconverted and can be used as anetch stop. In the example of FIG. 19, the process begins at 1910 withconformal deposition of an initial boron layer 1925 in the feature toclose off the pinch points, leaving a void 1912. Examples of compoundsthat may be used to deposit boron are described above. Part of the boronlayer 1925 is then converted to a tungsten layer 1927 a at 1920. Asnoted above, in some implementations, boron up to a certain limit (e.g.,10 nm) is converted. The partial conversion leaves a residual boronlayer 1925 a. The tungsten layer 1927 a is then selectively removed,leaving boron layer 1925 a, at 1930. The boron layer 1925 a is thenpartially converted to tungsten, forming tungsten layer 1927 b andresidual boron layer 1925 b at 1940. In this example, boron is convertedjust through the pinch point so that the feature will open up in asubsequent W-selective etch. In some other implementations, one or moreadditional partial conversions/selective etches may be performed to openthe feature due to the self-limiting nature of the conversion. Thetungsten layer 1927 b is selectively removed and in a subsequentoperation, the remaining boron layer 1925 b is converted to tungstenlayer 1927 c. Tungsten layer 1927 c can then be the basis for conformaldeposition to fill the feature (e.g., as in FIG. 16) or selectivedeposition to fill the feature (e.g., as in FIG. 14).

FIG. 20 shows a sequence described in U.S. patent application Ser. No.13/774,350, incorporate by reference herein, in which non-conformalselective inhibition is used to fill in the interior of the featurebefore pinch off. The selective inhibition technique discussed may beused with one or more of the techniques described herein. In FIG. 20, atungsten nucleation layer 2004 is conformally deposited on anunder-layer 2013 at 2010. A PNL process as described above can be used.Note that in some implementations, this operation of depositing aconformal nucleation layer may be omitted. Next, the feature is exposedto an inhibition chemistry to selectively inhibit portions 2006 at 2020.In this example, the portions 2008 through pillar constrictions 2051 areselectively inhibited. Inhibition can involve for example, exposure to adirect (in-situ) plasma generated from a gas such as N₂, H₂, forminggas, NH₃, O₂, CH₄, etc. Other methods of exposing the feature toinhibition species are described further below. Next, a CVD process isperformed to selectively deposit tungsten in accordance with theinhibition profile: bulk tungsten 2008 is preferentially deposited onthe non-inhibited portions of the nucleation layer 2004, such thathard-to-fill regions behind constrictions are filled, at 2030. Theremainder of the feature is then filled with bulk tungsten 2009 at 2040.The same CVD process used to selectively deposit tungsten may be used toremainder of the feature, or a different CVD process using a differentchemistry or process conditions and/or performed after a nucleationlayer is deposited may be used.

According to various implementations, any of the above examples mayemploy conformal or non-conformal etches to tailor feature fillaccording to various implementations. FIG. 21 shows an example offeature fill using a non-conformal etch. In the example of FIG. 21, PNLnucleation plus CVD W can be used to deposit a thin conformal layer oftungsten 2102 in the feature at 2110. This is followed by anon-conformal etch, with high selectivity to protect the under-layer2113, at 2120. For example, a non-conformal etch having high W:TiNselectivity as described with reference to FIG. 9B may be performed forTiN under-layers. This leaves tungsten layer 2002 in the interior 2153of the feature, and removes it near the feature ends 2155. CVD Wdeposition of another thin layer of tungsten 2103 at 2130 is followed byanother non-conformal, W-selective etch. These dep-etch-dep operationscan be repeated to fill the feature at 2140. According to variousimplementations, each subsequent deposition operation may or may notinclude deposition of a nucleation layer for conformal or selectivedeposition. In some implementations, nucleation delay (passivation),e.g., at high source power, can be used during CVD W to inhibit growthnear the opening.

In some implementations, fluorine-free tungsten and tungsten nitridefilms may be used to reduce fluorine-based processing andfluorine-containing byproducts in tungsten feature fill. FIG. 22 showsan example of sequence in which a thermal ALD fluorine-free tungstennitride (FFWN) film may be converted to fluorine free tungsten (FFW) infilling a feature. The sequence begins at 2210 with deposition of a FFWNlayer by a thermal ALD or PNL, as described above with reference toFIGS. 13C and 13D. The FFWN layer is deposited without completelypinching off the interior of the structure to allow nitrogen gas toescape. The FFWN is then converted to FFW during a thermal anneal, withN₂ gas leaving at 2220. In the depicted example, a FFWN or FFW cap layer2208 is then deposited to close of the feature interior 2253. Dependingon the thickness of the cap layer 2208, a thermal anneal may beperformed to remove convert a FFWN cap layer 2208 to FFW. In someimplementations, the cap layer 2208 may be thin enough that a negligibleamount of nitrogen is present in the tungsten-filled feature and noanneal is performed. It should be noted that in some implementations,cap layer 2208 may close off the interior 2253 prior to deposition ofthe layer within the feature. Unlike the sequence described below withreference to FIG. 23, this is acceptable from a fluorine managementperspective as no fluorine is used in the process. While the sequenceshown in FIG. 22 leaves a void 2212, in alternate implementations, oneor more techniques described above for reducing or eliminating voids maybe employed.

FIG. 23 shows an example of sequence in which a thermal ALDfluorine-free tungsten nitride (FFWN) or fluorine-free tungsten (FFW)film may be used in tungsten feature fill to seal a layer depositedusing fluorine. The sequence begins at 2310 with conformal deposition ofa tungsten layer 2302 using a fluorine- (or other halogen)-containingcompound. Conformal deposition may involve for example, deposition of atungsten nucleation layer followed by bulk deposition using tungstenhexafluoride or tungsten hexachloride. Deposition is halted prior topinch, in some implementations, leaving at least 5-10 nm between theapproaching sidewalls at the pinch point 2351. Next, at 2320, a pumpdown operation is performed to remove all of the fluorine-containingbyproduct such as HF. A FFWN or FFW layer 2308 is then deposited tocover the tungsten layer 2302. In some implementations, this includesdepositing the layer 2308 within the interior of the feature 2353 tohelp prevent the release of any fluorine present in the tungsten layer2302. While the sequence shown in FIG. 23 leaves a void 2312, inalternate implementations, one or more techniques described above forreducing or eliminating voids may be employed.

According to various implementations, the etches described in theprocess sequences above can be conformal, mildly non-conformal or highlynon-conformal as described above with respect to FIGS. 9A and 9B,according to the desired etch profile. For example, etches used to openup a pinch-off feature may use process conditions that produce conformaletches.

Nucleation Layer Deposition

In some implementations, the methods described herein involve depositionof a tungsten nucleation layer prior to deposition of a bulk layer. Anucleation layer is typically a thin conformal layer that facilitatessubsequent deposition of bulk tungsten-containing material thereon.According to various implementations, a nucleation layer may bedeposited prior to any fill of the feature and/or at subsequent pointsduring fill of the feature. For example, in some implementations, anucleation layer may be deposited following etch of tungsten in afeature.

In certain implementations, the nucleation layer is deposited using apulsed nucleation layer (PNL) technique. In a PNL technique, pulses of areducing agent, optional purge gases, and tungsten-containing precursorare sequentially injected into and purged from the reaction chamber. Theprocess is repeated in a cyclical fashion until the desired thickness isachieved. PNL broadly embodies any cyclical process of sequentiallyadding reactants for reaction on a semiconductor substrate, includingatomic layer deposition (ALD) techniques. PNL techniques for depositingtungsten nucleation layers are described in U.S. Pat. Nos. 6,635,965;7,005,372; 7,141,494; 7,589,017, 7,772,114, 7,955,972 and 8,058,170, andU.S. Patent Publication No. 2010-0267235, all of which are incorporatedby reference herein in their entireties. Nucleation layer thickness candepend on the nucleation layer deposition method as well as the desiredquality of bulk deposition. In general, nucleation layer thickness issufficient to support high quality, uniform bulk deposition. Examplesmay range from 10 Å-100 Å.

While examples of PNL deposition are provided above, the methodsdescribed herein are not limited to a particular method of tungstennucleation layer deposition, but include deposition of bulk tungstenfilm on tungsten nucleation layers formed by any method including PNL,ALD, CVD, and physical vapor deposition (PVD). Moreover, in certainimplementations, bulk tungsten may be deposited directly in a featurewithout use of a nucleation layer. For example, in some implementations,the feature surface and/or an already-deposited under-layer supportsbulk tungsten deposition. In some implementations, a bulk tungstendeposition process that does not use a nucleation layer may beperformed. U.S. patent application Ser. No. 13/560,688, filed Jul. 27,2012, incorporated by reference herein, describes deposition of atungsten bulk layer without a nucleation layer, for example.

In various implementations, tungsten nucleation layer deposition caninvolve exposure to a tungsten-containing precursor such as tungstenhexafluoride (WF₆), tungsten hexachloride (WCl₆), and tungstenhexacarbonyl (W(CO)₆). In certain implementations, thetungsten-containing precursor is a halogen-containing compound, such asWF₆. Organo-metallic precursors, and precursors that are free offluorine such as MDNOW(methylcyclopentadienyl-dicarbonylnitrosyl-tungsten) and EDNOW(ethylcyclopentadienyl-dicarbonylnitrosyl-tungsten) may also be used.

Examples of reducing agents can include boron-containing reducing agentsincluding diborane (B₂H₆) and other boranes, silicon-containing reducingagents including silane (SiH₄) and other silanes, hydrazines, andgermanes. In some implementations, pulses of tungsten-containingprecursors can be alternated with pulses of one or more reducing agents,e.g., S/W/S/W/B/W, etc., W represents a tungsten-containing precursor, Srepresents a silicon-containing precursor, and B represents aboron-containing precursor. In some implementations, a separate reducingagent may not be used, e.g., a tungsten-containing precursor may undergothermal or plasma-assisted decomposition.

According to various implementations, hydrogen may or may not be run inthe background. Further, in some implementations, deposition of atungsten nucleation layer may be followed by one or more treatmentoperations prior to tungsten bulk deposition. Treating a depositedtungsten nucleation layer to lower resistivity is described for examplein U.S. Pat. Nos. 7,772,114 and 8,058,170 and U.S. Patent PublicationNo. 2010-0267235, incorporated by reference herein.

Bulk Deposition

In many implementations, tungsten bulk deposition can occur by a CVDprocess in which a reducing agent and a tungsten-containing precursorare flowed into a deposition chamber to deposit a bulk fill layer in thefeature. An inert carrier gas may be used to deliver one or more of thereactant streams, which may or may not be pre-mixed. Unlike PNL or ALDprocesses, this operation generally involves flowing the reactantscontinuously until the desired amount is deposited. In certainimplementations, the CVD operation may take place in multiple stages,with multiple periods of continuous and simultaneous flow of reactantsseparated by periods of one or more reactant flows diverted.

Various tungsten-containing gases including, but not limited to, WF₆,WCl₆, and W(CO)₆ can be used as the tungsten-containing precursor. Incertain implementations, the tungsten-containing precursor is ahalogen-containing compound, such as WF₆. In certain implementations,the reducing agent is hydrogen gas, though other reducing agents may beused including silane (SiH₄), disilane (Si₂H₆) hydrazine (N₂H₄),diborane (B₂H₆) and germane (GeH₄). In many implementations, hydrogengas is used as the reducing agent in the CVD process. In some otherimplementations, a tungsten precursor that can decompose to form a bulktungsten layer can be used. Bulk deposition may also occur using othertypes of processes including ALD processes.

Examples of temperatures may range from 200° C. to 500° C. According tovarious implementations, any of the CVD W operations described hereincan employ a low temperature CVD W fill, e.g., at about 250° C.-350° C.or about 300° C.

Deposition may proceed according to various implementations until acertain feature profile is achieved and/or a certain amount of tungstenis deposited. In some implementations, the deposition time and otherrelevant parameters may be determined by modeling and/or trial anderror. For example, for an initial deposition for an inside out fillprocess in which tungsten can be conformally deposited in a featureuntil pinch-off, it may be straightforward to determine based on thefeature dimensions the tungsten thickness and corresponding depositiontime that will achieve pinch-off. In some implementations, a processchamber may be equipped with various sensors to perform in-situmetrology measurements for end-point detection of a depositionoperation. Examples of in-situ metrology include optical microscopy andX-Ray Fluorescence (XRF) for determining thickness of deposited films.

It should be understood that the tungsten films described herein mayinclude some amount of other compounds, dopants and/or impurities suchas nitrogen, carbon, oxygen, boron, phosphorous, sulfur, silicon,germanium and the like, depending on the particular precursors andprocesses used. The tungsten content in the film may range from 20% to100% (atomic) tungsten. In many implementations, the films aretungsten-rich, having at least 50% (atomic) tungsten, or even at leastabout 60%, 75%, 90%, or 99% (atomic) tungsten. In some implementations,the films may be a mixture of metallic or elemental tungsten (W) andother tungsten-containing compounds such as tungsten carbide (WC),tungsten nitride (WN), etc.

CVD and ALD deposition of these materials can include using anyappropriate precursors. For example, CVD and ALD deposition of tungstennitride can include using halogen-containing and halogen-freetungsten-containing and nitrogen-containing compounds as describedfurther below. CVD and ALD deposition of titanium-containing layers caninclude using precursors containing titanium with examples includingtetrakis(dimethylamino)titanium (TDMAT) and titanium chloride (TiCl₄),and if appropriate, one or more co-reactants. CVD and ALD deposition oftantalum-containing layers can include using precursors such aspentakis-dimethylamino tantalum (PDMAT) and TaF₅ and, if appropriate,one or more co-reactants CVD and ALD deposition of cobalt-containinglayers can include using precursors such asTris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt,bis(cyclopentadienyl)cobalt, and dicobalt hexacarbonyl butylacetylene,and one or more co-reactants. CVD and ALD deposition ofnickel-containing layers can include using precursors such ascyclopentadienylallylnickel (CpAllylNi) and MeCp₂Ni. Examples ofco-reactants can include N₂, NH₃, N₂H₄, N₂H₆, SiH₄, Si₃H₆, B₂H₆, H₂, andAlCl₃.

Tungsten Etch

Etching tungsten can be performed by exposing the tungsten to one ormore etchant species that can react with tungsten. Examples of etchantspecies include halogen species and halogen-containing species. Exampleof initial etchant materials that can be used for removal oftungsten-containing materials include nitrogen tri-fluoride (NF₃),tetra-fluoro-methane (CF₄), tetrafluoroethylene (C₂F₄), hexafluoroethane(C₂F₆), and octafluoropropane (C₃F₈), tri-fluoro-methane (CHF₃),chlorotrifluoromethane (CF₃Cl), sulfur hexafluoride (SF₆), and molecularfluorine (F₂). In some implementations, the species can be activated andinclude radicals and/or ions. For example, an initial etchant materialmay be flown through a remote plasma generator and/or subjected to anin-situ plasma. In some implementations, the tungsten may be exposed tonon-plasma etchant vapor.

In addition to the examples given above, any known etchant chemistry maybe used for etching non-tungsten-containing films as well astungsten-containing films. For example, fluorine-containing compoundssuch as NF₃, may be used for titanium-containing compounds such as TiNand TiC. Chlorine-containing compounds such as Cl₂ and BCl₃ may be usedin some implementations, for example to etch TiAl, TiAlN,nickel-containing compounds and cobalt-containing compounds. Further,although etching below refers chiefly to plasma and/or non-plasma vaporphase etching, in some implementations, the methods may also beimplemented with wet etching techniques.

In some implementations, a remotely generated plasma may be used. Theinitial etchant material and, in certain implementations, inert gases,such as argon, helium and others, can be supplied to any suitable remoteplasma generator. For example, remote plasma units, such as ASTRON® iType AX7670, ASTRON® e Type AX7680, ASTRON® ex Type AX7685, ASTRON® hf-sType AX7645, all available from MKS Instruments of Andover, Mass., maybe used. A remote plasma unit is typically a self-contained devicegenerating weakly ionized plasma using the supplied etchant. In someimplementations, a high power radio frequency (RF) generator providesenergy to the electrons in the plasma. This energy is then transferredto the neutral etchant molecules leading to temperature on the order of2000K causing thermal dissociation of these molecules. A remote plasmaunit may dissociate more than 60% of incoming etchant molecules becauseof its high RF energy and special channel geometry causing the etchantto adsorb most of this energy.

In some implementations, the activated species from the remote plasmaunit delivered to the chamber in which the etch is performed areradicals and include substantially no ionic species. One of ordinaryskill in the art will understand that there may be some small number ofionic species that do not contribute to the etch. This amount may besmall enough to be undetectable. In some implementations, the activatedspecies from the remote plasma unit delivered to the chamber may includea substantial number of ionic species in addition to radical species.

In some implementations, an etching operation may use a plasma generatedin situ in the chamber housing the substrate such that the tungsten inexposed to a direct plasma, in addition to or instead of a remotelygenerated plasma. In some implementations, a radio frequency (RF) plasmagenerator may be used to generate a plasma between two electrodes thechamber. Examples of electrodes include a shower head and a pedestal,for example. In one example, a High Frequency (HF) generator capable ofproviding between about 0 W and 10,000 W at frequencies between about 1MHz and 100 MHz may be used. In a more specific implementation, the HFgenerator may deliver between about 0 W to 5,000 W at about 13.56 MHz.In some implementations, a Low Frequency (LF) generator capable ofproviding between about 0 and 10,000 W at frequencies between about 100kHz and 2 MHz, or between about 100 kHz and 1 MHz, e.g. 400 kHz may beused.

The plasma generator may be a capacitively coupled plasma (CCP)generator, an inductively coupled plasma (ICP) generator, a transformercoupled plasma (TCP) generator, an electron cyclotron resonance (ECR)generator, or a helicon plasma generator. In addition to RF sources,microwave sources may be used.

According to various implementations, some or all etch operations can beperformed in the same chamber in which other operations includingdeposition and/or treatment operations are performed, or in a dedicatedetch chamber. If a dedicated etch chamber is used, it may be connectedto the same vacuum environment of one or more other processing chamber,or be part of a separate vacuum environment. For example, TCP etchmodule such as the Kiyo® conductor etch module available from LamResearch Corporation may be used in some implementations. Exampleetchants that may be used with such a module include NF₃, CF₄, SF₆,CH₃F, CH₂F₂, and CF₄. Example operating pressures can range from 30mTorr to 100 mTorr. Example temperatures can range from 30° C. to 120°C.

In various implementations, etching is performed until a certaincharacteristic of the deposited tungsten is removed or a certain profileis achieved. For example, with inside-out fill techniques describedabove, the etch may proceed until the pinched-off tungsten is removed,or until a seam is removed. In some implementations, the etch endpointfor particular etch process parameters may be determined by modelingand/or trial and error for a particular feature geometry and the profileand amount of deposited tungsten being etched. In some implementations,a process chamber may be equipped with various sensors to performin-situ metrology measurements to identify the extent of removal.Examples of in-situ metrology include optical microscopy and XRF fordetermining thickness of films. Further, infrared (IR) spectroscopy maybe used to detect amounts of tungsten fluoride (WFx) or other byproductsgenerated during etching. In some implementations, an under-layer may beused as an etch-stop layer. Optical emission spectroscopy (OES) may alsobe used to monitor the etch. According to various implementations, anetch of tungsten may be more or less preferential (or non-preferential)to an under-layer. For example, an etch can be preferential to W with,for example, a Ti or TiN underlayer acting as an etch stop. In someimplementations, the etch can etch W and Ti or TiN with an underlyingdielectric acting as an etch stop. Methods of tuning etchpreferentiality with respect to an under-layer are described above.

Also, according to various implementations, the conformality of anetching operation may be modulated. A conformal etch is an etch in whichmaterial is removed uniformly through-out the feature. Methods ofmodulating etch conformality are described above. In someimplementations, modulating etch conformality can include operating ornot operating in a mass transport limited regime. In such a regime, theremoval rate inside the feature is limited by amounts of and/or relativecompositions of different etching material components (e.g., an initialetchant material, activated etchant species, and recombined etchantspecies) that diffuse into the feature. In certain examples, etchingrates depend on various etchant components' concentrations at differentlocations inside the feature. It should be noted that the terms“etching” and “removal” are used interchangeably in this document.

As described in U.S. patent application Ser. No. 13/016,656,incorporated by reference herein, mass transport limiting conditions maybe characterized, in part, by overall etchant concentration variations.In certain embodiments, this concentration is less inside the featurethan near its opening resulting in a higher etching rate near theopening than inside. This in turn leads to selective removal. Masstransport limiting process conditions may be achieved by supplyinglimited amounts of etchant into the processing chamber (e.g., use lowetchant flow rates relative to the cavity profile and dimensions), whilemaintaining relative high etching rates in order to consume some etchantas it diffuses into the feature. In certain embodiment, a concentrationgradient is substantial, which may be caused relatively high etchingkinetics and relative low etchant supply. In certain embodiments, anetching rate near the opening may also be mass limited, but thiscondition is not required to achieve selective removal.

In addition to the overall etchant concentration variations inside highaspect ratio features, etching conformality may be influenced byrelative concentrations of different etchant components throughout thefeature. These relative concentrations in turn depend by relativedynamics of dissociation and recombination processes of the etchingspecies. An initial etchant material is typically passed through aremote plasma generator and/or subjected to an in-situ plasma in orderto generate activated etchant species (e.g., fluorine atoms, radicals).However, activated specifies tend to recombine into less activerecombined etching species (e.g., fluorine molecules) and/or react withtungsten-containing materials along their diffusion paths. As such,different parts of the deposited tungsten-containing layer may beexposed to different concentrations of different etchant materials,e.g., an initial etchant, activated etchant species, and recombinedetchant species. This provides additional opportunities for controllingetching conformality.

For example, activated fluorine species are generally more reactive withtungsten-containing materials than initial etching materials andrecombined etching materials. Furthermore, the activated fluorinespecies may be generally less sensitive to temperature variations thanthe recombined fluorine species. Therefore, in some implementations,process conditions may be controlled in such a way that removal ispredominantly attributed to activated fluorine species, predominantlyattributed to recombined species, or includes both fluorine andrecombined species. Furthermore, specific process conditions may resultin activated fluorine species being present at higher concentrationsnear features' openings than inside the features. For example, someactivated species may be consumed (e.g., react with deposited materialsand/or adsorbed on its surface) and/or recombined while diffusing deeperinto the features, especially in small high aspect ratio features. Itshould be noted that recombination of activated species also occursoutside of high aspect ratio features, e.g., in the showerhead of theprocessing chamber, and depends on a chamber pressure. Therefore, achamber pressure may be controlled to adjust concentrations of activatedetching species at various points of the chamber and features.

Flow rates of the etchant typically depend on a size of the chamber,etching rates, etching uniformity, and other parameters. For example, aflow rate can be selected in such a way that more tungsten-containingmaterial is removed near the opening than inside the feature or thattungsten-containing material is removed uniformly through a feature orportion of a feature. For example, a flow rate for a 195-liter chamberper station may be between about 25 sccm and 10,000 sccm or, in morespecific embodiments, between about 50 sccm and 1,000 sccm. In certainembodiments, the flow rate is less than about 2,000 sccm, less thanabout 1,000 sccm, or more specifically less than about 500 sccm. Itshould be noted that these values are presented for one individualstation configured for processing a 300-mm wafer substrate. These flowrates can be scaled up or down depending on a substrate size, a numberof stations in the apparatus (e.g., quadruple for a four stationapparatus), a processing chamber volume, and other factors.

A temperature for the substrate can be selected in such a way to notonly induce a chemical reaction between the deposited layer and variousetchant species but also to control the rate of the reaction between thetwo. For example, a temperature may be selected to have high removalrates such that more material is removed near the opening than insidethe feature or low removal rates such that material is removed fromwithin the feature. Furthermore, a temperature may be also selected tocontrol recombination of activated species (e.g., recombination ofatomic fluorine into molecular fluorine) and/or control which species(e.g., activated or recombined species) contribute predominantly toetching. The substrate temperature may be selected based on etchantchemical compositions, a desired etching rate, desired concentrationdistributions of activated species, desired contributions to selectiveremoval by different species, and other material and process parameters.In certain embodiments, a substrate is maintained at less than about300° C., or more particularly at less than about 250° C., or less thanabout 150° C., or even less than about 100° C. In other embodiments, asubstrate is heated to between about 300° C. and 450° C. or, in morespecific embodiments, to between about 350° C. and 400° C. While thesetemperature ranges are provide for F-based etches, other temperatureranges may be used for different types of etchants.

Activation energy of activated fluorine species is much less than thatof the recombined fluorine. Therefore, lowering substrate temperaturesmay result in more removal contribution from activated species. Atcertain temperatures (and other process conditions, e.g., flow rates andchamber pressures), a relative removal contribution of the activatedspecies may exceed that of the recombined species.

Distribution of a material within a feature may also be characterized byits step coverage. For the purposes of this description, “step coverage”is defined as a ratio of two thicknesses, i.e., the thickness of thematerial inside the feature divided by the thickness of the materialnear the opening. For purposes of this document, the term “inside thefeature” represents a middle portion of the feature located about themiddle point of the feature along the feature's axis, e.g., an areabetween about 25% and 75% of the distance or, in certain embodiments,between about 40% and 60% of the distance along the feature's depthmeasured from the feature's opening, or an end portion of the featurelocated between about 75% and 95% of the distance along the feature'saxis as measured from the opening. The term “near the opening of thefeature” or “near the feature's opening” represents a top portion of thefeature located within 25% or, more specifically, within 10% of theopening's edge or other element representative of the opening's edge.Step coverage of over 100% can be achieved, for example, by filling afeature wider in the middle or near the bottom of the feature than atthe feature opening.

As discussed above, etch conformality may be modulated such than anetched layer has a target step coverage depending on the particulararchitecture of the feature. In certain embodiments, a targeted stepcoverage of the etched layer is at least about 60%, 75%, 100%, orsuper-conformal (over 100%), such as 125%. In certain embodiments, astep coverage below about 50%, 25% or less may be targeted.

Selective Inhibition of Tungsten Nucleation

As described in U.S. patent application Ser. No. 13/774,350,incorporated by reference herein, selective inhibition can involveexposure to activated species that passivate the feature surfaces. Forexample, in certain implementations, a tungsten (W) surface can bepassivated by exposure to a nitrogen-based or hydrogen-based plasma. Insome implementations, inhibition can involve a chemical reaction betweenactivated species and the feature surface to form a thin layer of acompound material such as tungsten nitride (WN) or tungsten carbide(WC). In some implementations, inhibition can involve a surface effectsuch as adsorption that passivates the surface without forming a layerof a compound material. Activated species may be formed by anyappropriate method including by plasma generation and/or exposure toultraviolet (UV) radiation. In some implementations, the substrateincluding the feature is exposed to a plasma generated from one or moregases fed into the chamber in which the substrate sits. In someimplementations, one or more gases may be fed into a remote plasmagenerator, with activated species formed in the remote plasma generatorfed into a chamber in which the substrate sits. The plasma source can beany type of source including radio frequency (RF) plasma source ormicrowave source. The plasma can be inductively and/orcapacitively-coupled. Activated species can include atomic species,radical species, and ionic species. In certain implementations, exposureto a remotely-generated plasma includes exposure to radical and atomizedspecies, with substantially no ionic species present in the plasma suchthat the inhibition process is not ion-mediated. In otherimplementations, ion species may be present in a remotely-generatedplasma. In certain implementations, exposure to an in-situ plasmainvolves ion-mediated inhibition.

For tungsten (W) surfaces, exposure to nitrogen-based and/orhydrogen-based plasmas inhibits subsequent tungsten deposition on the Wsurfaces. Other chemistries that may be used for inhibition of tungstensurfaces include oxygen-based plasmas and hydrocarbon-based plasmas. Forexample, molecular oxygen or methane may be introduced to a plasmagenerator. As used herein, a nitrogen-based plasma is a plasma in whichthe main non-inert component is nitrogen. An inert component such asargon, xenon, or krypton may be used as a carrier gas. In someimplementations, no other non-inert components are present in the gasfrom which the plasma is generated except in trace amounts. In someimplementations, inhibition chemistries may be nitrogen-containing,hydrogen-containing, oxygen-containing, and/or carbon-containing, withone or more additional reactive species present in the plasma.

In U.S. patent application Ser. No. 13/351,970, for example, nitridationof a feature surface to selectively passivate the surface is described.Using a NF₃ plasma, for example, where activated fluorine radicals reactwith and remove tungsten at the feature opening, the nitrogen generatedfrom the NF₃ plasma can cause nitridation of the tungsten surfaceforming tungsten nitride. Subsequent deposition of tungsten on anitrided surface is significantly delayed, compared to on a regular bulktungsten film. A longer delay allows the feature to stay open for longerbefore pinching off, and promoting fill improvement because more WF₆molecules can reach the inside of the feature and deposit tungsten. Thisis illustrated in FIG. 11, which shows a partially filled feature 1101including an overhang 1115. During an NF₃ plasma etch, more nitrogenspecies (e.g., nitrogen radicals) are present at 1103 near the top ofthe feature, than at 1105, further within the feature. As a result W—Nforms at the top of the feature, but in the feature interior. Duringcomplete fill, tungsten deposits more readily on the tungsten (W)surface within the feature than on the W—N surface at the top of thefeature. This allows the feature 1101 to stay open longer at 1107,promoting fill improvement.

In addition to NF₃, fluorocarbons such as CF₄ or C₂F₈ may be used.However, in certain implementations, the inhibition species arefluorine-free to prevent etching during selective inhibition.

In certain implementations, UV radiation and/or thermal energy may beused instead of or in addition to plasma generators to provide activatedspecies. In addition to tungsten surfaces, nucleation may be inhibitedon liner/barrier layers surfaces such as TiN and/or WN surfaces. Anychemistry that passivates these surfaces may be used. For TiN and WN,this can include exposure to nitrogen-based or nitrogen-containingchemistries. In certain implementations, the chemistries described abovefor W may also be employed for TiN, WN, or other liner layer surfaces.

Tuning an inhibition profile can involve appropriately controlling aninhibition chemistry, substrate bias power, plasma power, processpressure, exposure time, and other process parameters. For in situplasma processes (or other processes in which ionic species arepresent), a bias can be applied to the substrate. Substrate bias can, insome implementations, significantly affect an inhibition profile, withincreasing bias power resulting in active species deeper within thefeature. For 3-D structures in which selectivity is desired in a lateraldirection (tungsten deposition preferred in the interior of thestructure), but not in a vertical direction, increased bias power can beused to promote top-to-bottom deposition uniformity.

While bias power can be used in certain implementations as the primaryor only knob to tune an inhibition profile for ionic species, in certainsituations, other performing selective inhibition uses other parametersin addition to or instead of bias power. These include remotelygenerated non-ionic plasma processes and non-plasma processes. Also, inmany systems, a substrate bias can be easily applied to tune selectivityin vertical but not lateral direction. Accordingly, for 3-D structuresin which lateral selectivity is desired, parameters other than bias maybe controlled, as described above.

Inhibition chemistry can also be used to tune an inhibition profile,with different ratios of active inhibiting species used. For example,for inhibition of W surfaces, nitrogen may have a stronger inhibitingeffect than hydrogen; adjusting the ratio of N₂ and H₂ gas in a forminggas-based plasma can be used to tune a profile. The plasma power mayalso be used to tune an inhibition profile, with different ratios ofactive species tuned by plasma power. For example, in certainimplementations described herein, nitrogen radical formation andresultant W—N formation and the related passivation effect can bemodulated by varying the plasma power. Varying plasma power can alsoallow control of the resistivity of the final W film. FIG. 12 is a graphdemonstrating the ability to control subsequent deposition delay time byvarying the etch power. It can be understood that any power between“high” and “low” can be used to control the delay as desired. In FIG.12, a remotely-generated plasma etch using NF₃ at low power resulted inreduced nucleation delay (faster nucleation) in a subsequent deposition,than a higher power remotely-generated plasma etch. This may be due tothe presence of more nitrogen species during the high plasma power etch,increasing the formation of WN and the subsequent delay.

Process pressure can be used to tune a profile, as pressure can causemore recombination (deactivating active species) as well as pushingactive species further into a feature. Process time may also be used totune inhibition profiles, with increasing treatment time causinginhibition deeper into a feature.

In some implementations, selective inhibition can be achieved by in amass transport limited regime. In this regime, the inhibition rateinside the feature is limited by amounts of and/or relative compositionsof different inhibition material components (e.g., an initial inhibitionspecies, activated inhibition species, and recombined inhibitionspecies) that diffuse into the feature. In certain examples, inhibitionrates depend on various components' concentrations at differentlocations inside the feature.

Mass transport limiting conditions may be characterized, in part, byoverall inhibition concentration variations. In certain implementations,a concentration is less inside the feature than near its openingresulting in a higher inhibition rate near the opening than inside. Thisin turn leads to selective inhibition near the feature opening. Masstransport limiting process conditions may be achieved by supplyinglimited amounts of inhibition species into the processing chamber (e.g.,use low inhibition gas flow rates relative to the cavity profile anddimensions), while maintaining relative high inhibition rates near thefeature opening to consume some activated species as they diffuse intothe feature. In certain implementation, a concentration gradient issubstantial, which may be caused relatively high inhibition kinetics andrelatively low inhibition supply. In certain implementations, aninhibition rate near the opening may also be mass transport limited,though this condition is not required to achieve selective inhibition.

In addition to the overall inhibition concentration variations insidefeatures, selective inhibition may be influenced by relativeconcentrations of different inhibition species throughout the feature.These relative concentrations in turn can depend on relative dynamics ofdissociation and recombination processes of the inhibition species. Asdescribed above, an initial inhibition material, such as molecularnitrogen, can be passed through a remote plasma generator and/orsubjected to an in-situ plasma to generate activated species (e.g.,atomic nitrogen, nitrogen ions). However, activated species mayrecombine into less active recombined species (e.g., nitrogen molecules)and/or react with W, WN, TiN, or other feature surfaces along theirdiffusion paths. As such, different parts of the feature may be exposedto different concentrations of different inhibition materials, e.g., aninitial inhibition gas, activated inhibition species, and recombinedinhibition species. This provides additional opportunities forcontrolling selective inhibition. For example, activated species aregenerally more reactive than initial inhibition gases and recombinedinhibition species. Furthermore, in some cases, the activated speciesmay be less sensitive to temperature variations than the recombinedspecies. Therefore, process conditions may be controlled in such a waythat removal is predominantly attributed to activated species. As notedabove, some species may be more reactive than others. Furthermore,specific process conditions may result in activated species beingpresent at higher concentrations near features' openings than inside thefeatures. For example, some activated species may be consumed (e.g.,reacted with feature surface materials and/or adsorbed on the surface)and/or recombined while diffusing deeper into the features, especiallyin small high aspect ratio features. Recombination of activated speciescan also occur outside of features, e.g., in the showerhead or theprocessing chamber, and can depends on chamber pressure. Therefore,chamber pressure may be specifically controlled to adjust concentrationsof activated species at various points of the chamber and features.

Flow rates of the inhibition gas can depend on a size of the chamber,reaction rates, and other parameters. A flow rate can be selected insuch a way that more inhibition material is concentrated near theopening than inside the feature. In certain implementations, these flowrates cause mass-transport limited selective inhibition. For example, aflow rate for a 195-liter chamber per station may be between about 25sccm and 10,000 sccm or, in more specific implementations, between about50 sccm and 1,000 sccm. In certain implementations, the flow rate isless than about 2,000 sccm, less than about 1,000 sccm, or morespecifically less than about 500 sccm. It should be noted that thesevalues are presented for one individual station configured forprocessing a 300-mm substrate. These flow rates can be scaled up or downdepending on a substrate size, a number of stations in the apparatus(e.g., quadruple for a four station apparatus), a processing chambervolume, and other factors.

In certain implementations, the substrate can be heated up or cooleddown before selective inhibition. A predetermined temperature for thesubstrate can be selected to induce a chemical reaction between thefeature surface and inhibition species and/or promote adsorption of theinhibition species, as well as to control the rate of the reaction oradsorption. For example, a temperature may be selected to have highreaction rate such that more inhibition occurs near the opening thaninside the feature. Furthermore, a temperature may be also selected tocontrol recombination of activated species (e.g., recombination ofatomic nitrogen into molecular nitrogen) and/or control which species(e.g., activated or recombined species) contribute predominantly toinhibition. In certain implementations, a substrate is maintained atless than about 300° C., or more particularly at less than about 250°C., or less than about 150° C., or even less than about 100° C. In otherimplementations, a substrate is heated to between about 300° C. and 450°C. or, in more specific implementations, to between about 350° C. and400° C. Other temperature ranges may be used for different types ofinhibition chemistries. Exposure time can also be selected to causeselective inhibition. Example exposure times can range from about 10 sto 500 s, depending on desired selectivity and feature depth.

Apparatus

Any suitable chamber may be used to implement this novel method.Examples of deposition apparatuses include various systems, e.g., ALTUSand ALTUS Max, available from Novellus Systems, Inc. of San Jose,Calif., or any of a variety of other commercially available processingsystems.

FIG. 24 illustrates a schematic representation of an apparatus 2400 forprocessing a partially fabricated semiconductor substrate in accordancewith certain embodiments. The apparatus 2400 includes a chamber 2418with a pedestal 2420, a shower head 2414, and an in-situ plasmagenerator 2416. The apparatus 2400 also includes a system controller2422 to receive input and/or supply control signals to various devices.

The etchant and, in certain embodiments, inert gases, such as argon,helium and others, are supplied to the remote plasma generator 2406 froma source 2402, which may be a storage tank. Any suitable remote plasmagenerator may be used for activating the etchant before introducing itinto the chamber 2418. For example, a Remote Plasma Cleaning (RPC)units, such as ASTRON® i Type AX7670, ASTRON® e Type AX7680, ASTRON® exType AX7685, ASTRON® hf-s Type AX7645, all available from MKSInstruments of Andover, Mass., may be used. An RPC unit is typically aself-contained device generating weakly ionized plasma using thesupplied etchant. Imbedded into the RPC unit a high power RF generatorprovides energy to the electrons in the plasma. This energy is thentransferred to the neutral etchant molecules leading to temperature inthe order of 2000K causing thermal dissociation of these molecules. AnRPC unit may dissociate more than 60% of incoming etchant moleculesbecause of its high RF energy and special channel geometry causing theetchant to adsorb most of this energy.

In certain embodiments, an etchant is flown from the remote plasmagenerator 2406 through a connecting line 2408 into the chamber 2418,where the mixture is distributed through the shower head 2414. In otherembodiments, an etchant is flown into the chamber 2418 directlycompletely bypassing the remote plasma generator 2406 (e.g., the system2400 does not include such generator). Alternatively, the remote plasmagenerator 2406 may be turned off while flowing the etchant into thechamber 2418, for example, because activation of the etchant is notneeded.

The shower head 2414 or the pedestal 2420 typically may have an internalplasma generator 2416 attached to it. In one example, the generator 2416is a High Frequency (HF) generator capable of providing between about 0W and 10,000 W at frequencies between about 1 MHz and 100 MHz. In a morespecific embodiment, the HF generator may deliver between about 0 W to5,000 W at about 13.56 MHz. The RF generator 2416 may generate in-situplasma to enhance removal of the initial tungsten layer. In certainembodiments, the RF generator 2416 is not used during the removaloperations of the process.

The chamber 2418 may include a sensor 2424 for sensing various processparameters, such as degree of deposition and etching, concentrations,pressure, temperature, and others. The sensor 2424 may provideinformation on chamber conditions during the process to the systemcontroller 2422. Examples of the sensor 2424 include mass flowcontrollers, pressure sensors, thermocouples, and others. The sensor2424 may also include an infra-red detector or optical detector tomonitor presence of gases in the chamber and control measures.

Deposition and selective removal operations generate various volatilespecies that are evacuated from the chamber 2418. Moreover, processingis performed at certain predetermined pressure levels the chamber 2418.Both of these functions are achieved using a vacuum outlet 2426, whichmay be a vacuum pump.

In certain embodiments, a system controller 2422 is employed to controlprocess parameters. The system controller 2422 typically includes one ormore memory devices and one or more processors. The processor mayinclude a CPU or computer, analog and/or digital input/outputconnections, stepper motor controller boards, etc. Typically there willbe a user interface associated with system controller 2422. The userinterface may include a display screen, graphical software displays ofthe apparatus and/or process conditions, and user input devices such aspointing devices, keyboards, touch screens, microphones, etc.

In certain embodiments, the system controller 2422 controls thesubstrate temperature, etchant flow rate, power output of the remoteplasma generator 2406, pressure inside the chamber 2418 and otherprocess parameters. The system controller 2422 executes system controlsoftware including sets of instructions for controlling the timing,mixture of gases, chamber pressure, chamber temperature, and otherparameters of a particular process. Other computer programs stored onmemory devices associated with the controller may be employed in someembodiments.

The computer program code for controlling the processes in a processsequence can be written in any conventional computer readableprogramming language: for example, assembly language, C, C++, Pascal,Fortran or others. Compiled object code or script is executed by theprocessor to perform the tasks identified in the program. The systemsoftware may be designed or configured in many different ways. Forexample, various chamber component subroutines or control objects may bewritten to control operation of the chamber components necessary tocarry out the described processes. Examples of programs or sections ofprograms for this purpose include process gas control code, pressurecontrol code, and plasma control code.

The controller parameters relate to process conditions such as, forexample, timing of each operation, pressure inside the chamber,substrate temperature, etchant flow rates, etc. These parameters areprovided to the user in the form of a recipe, and may be enteredutilizing the user interface. Signals for monitoring the process may beprovided by analog and/or digital input connections of the systemcontroller 2422. The signals for controlling the process are output onthe analog and digital output connections of the apparatus 2400.

Multi-Station Apparatus

FIG. 25A shows an example of a multi-station apparatus 2500. Theapparatus 2500 includes a process chamber 2501 and one or more cassettes2503 (e.g., Front Opening Unified Pods) for holding substrates to beprocessed and substrates that have completed processing. The chamber2501 may have a number of stations, for example, two stations, threestations, four stations, five stations, six stations, seven stations,eight stations, ten stations, or any other number of stations. Thenumber of stations in usually determined by a complexity of theprocessing operations and a number of these operations that can beperformed in a shared environment. FIG. 25A illustrates the processchamber 2501 that includes six stations, labeled 2511 through 2516. Allstations in the multi-station apparatus 2500 with a single processchamber 2503 are exposed to the same pressure environment. However, eachstation may have a designated reactant distribution system and localplasma and heating conditions achieved by a dedicated plasma generatorand pedestal, such as the ones illustrated in FIG. 24.

A substrate to be processed is loaded from one of the cassettes 2503through a load-lock 2505 into the station 2511. An external robot 2507may be used to transfer the substrate from the cassette 2503 and intothe load-lock 2505. In the depicted embodiment, there are two separateload locks 2505. These are typically equipped with substratetransferring devices to move substrates from the load-lock 2505 (oncethe pressure is equilibrated to a level corresponding to the internalenvironment of the process chamber 2503) into the station 2511 and fromthe station 2516 back into the load-lock 2505 for removal from theprocessing chamber 2503. An mechanism 2509 is used to transfersubstrates among the processing stations 2511-516 and support some ofthe substrates during the process as described below.

In certain embodiments, one or more stations may be reserved for heatingthe substrate. Such stations may have a heating lamp (not shown)positioned above the substrate and/or a heating pedestal supporting thesubstrate similar to one illustrated in FIG. 24. For example, a station2511 may receive a substrate from a load-lock and be used to pre-heatthe substrate before being further processed. Other stations may be usedfor filling high aspect ratio features including deposition and etchingoperations.

After the substrate is heated or otherwise processed at the station2511, the substrate is moved successively to the processing stations2512, 2513, 2514, 2515, and 2516, which may or may not be arrangedsequentially. The multi-station apparatus 2500 is configured such thatall stations are exposed to the same pressure environment. In so doing,the substrates are transferred from the station 2511 to other stationsin the chamber 2501 without a need for transfer ports, such asload-locks.

In certain embodiments, one or more stations may be used to fillfeatures with tungsten-containing materials. For example, stations 2512may be used for an initial deposition operation, station 2513 may beused for a corresponding selective removal operation. In the embodimentswhere a deposition-removal cycle is repeated, stations 2514 may be usedfor another deposition operations and station 2515 may be used foranother partial removal operation. Section 2516 may be used for thefinal filling operation. It should be understood that any configurationsof station designations to specific processes (heating, filling, andremoval) may be used.

As an alternative to the multi-station apparatus described above, themethod may be implemented in a single substrate chamber or amulti-station chamber processing a substrate(s) in a single processingstation in batch mode (i.e., non-sequential). In this aspect of theinvention, the substrate is loaded into the chamber and positioned onthe pedestal of the single processing station (whether it is anapparatus having only one processing station or an apparatus havingmulti-stations running in batch mode). The substrate may be then heatedand the deposition operation may be conducted. The process conditions inthe chamber may be then adjusted and the selective removal of thedeposited layer is then performed. The process may continue with one ormore deposition-removal cycles and with the final filling operation allperformed on the same station. Alternatively, a single station apparatusmay be first used to perform only one of the operation in the new method(e.g., depositing, selective removal, final filling) on multiple wafersafter which the substrates may be returned back to the same station ormoved to a different station (e.g., of a different apparatus) to performone or more of the remaining operations.

Multi-Chamber Apparatus

FIG. 25B is a schematic illustration of a multi-chamber apparatus 2520that may be used in accordance with certain embodiments. As shown, theapparatus 2520 has three separate chambers 2521, 2523, and 2525. Each ofthese chambers is illustrated with two pedestals. It should beunderstood that an apparatus may have any number of chambers (e.g., one,two, three, four, five, six, etc.) and each chamber may have any numberof chambers (e.g., one, two, three, four, five, six, etc.). Each chamber2521-525 has its own pressure environment, which is not shared betweenchambers. Each chamber may have one or more corresponding transfer ports(e.g., load-locks). The apparatus may also have a shared substratehandling robot 2527 for transferring substrates between the transferports one or more cassettes 2529.

As noted above, separate chambers may be used for depositing tungstencontaining materials and selective removal of these deposited materialsin later operations. Separating these two operations into differentchambers can help to substantially improve processing speeds bymaintaining the same environmental conditions in each chamber. In otherwords, a chamber does not need to change its environment from conditionsused for deposition to conditions used for selective removal and back,which may involve different precursors, different temperatures,pressures, and other process parameters. In certain embodiments, it isfaster to transfer partially manufactured semiconductor substratesbetween two or more different chambers than changing environmentalconditions of these chambers.

Patterning Method/Apparatus:

The apparatus/process described hereinabove may be used in conjunctionwith lithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallycomprises some or all of the following steps, each step enabled with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper.

1. (canceled)
 2. A method comprising: performing multiple cycles of afeature fill process to fill a feature on substrate, wherein each cyclecomprises a) conformally depositing a boron layer in the feature, theboron layer having a thickness of at least 1.5 nm and b) converting theboron layer in the feature to tungsten.
 3. The method of claim 1,wherein the feature is completely filled with tungsten.
 4. The method ofclaim 1, wherein the boron layer in at least one cycle of the multiplecycles has a thickness of at least 3 nm.
 5. The method of claim 1,wherein the boron layer in at least one cycle of the multiple cycles hasa thickness of at least 5 nm.
 6. The method of claim 1, wherein (b)comprises volumetric expansion of material in the feature.
 7. The methodof claim 1, wherein the feature includes a titanium nitride layer.
 8. Amethod comprising: providing a substrate including a feature;conformally depositing a reducing agent layer in the feature; convertinga portion of the boron layer in the feature to tungsten, leaving aremaining boron layer in the feature; selectively etching the tungstenwith respect to the remaining boron layer; and converting the remainingboron layer to tungsten.
 9. The method of claim 8, wherein the reducingagent layer has a lower etch rate than the tungsten in an etch chemistryand conditions employed to selectively etch the tungsten.
 10. The methodof claim 8, wherein the reducing agent layer is deposited in the featureprior to any tungsten deposition in the feature.
 11. The method of claim8, wherein the reducing agent layer is deposited in the feature afterinitial tungsten deposition in the feature.
 12. The method of claim 8,wherein the reducing agent layer is a boron layer.
 13. The method ofclaim 12, wherein selectively etching the tungsten with respect to theremaining boron layer comprises exposing the tungsten to afluorine-based remote plasma.
 14. The method of claim 8, whereinreducing agent layer is a silicon-containing layer, aphosphorous-containing layer, a boron-containing layer, or agermanium-containing layer.
 15. A method comprising: providing asubstrate including a feature having one or more feature openings,feature sidewalls, and a feature interior, conformally depositing afluorine-free tungsten nitride layer in the feature, wherein thefluorine-free tungsten nitride layer is deposited using a fluorine-freetungsten precursor; and converting the fluorine-free tungsten nitridelayer to a fluorine-free tungsten layer.
 16. The method of claim 15,wherein depositing the fluorine-free tungsten nitride layer furthercomprises sequentially pulsing a nitrogen-containing compound and thefluorine-free tungsten precursor into a chamber containing thesubstrate.
 17. The method of claim 15, wherein depositing thefluorine-free tungsten nitride layer further comprises sequentiallypulsing, in any order, the fluorine-free tungsten precursor, thenitrogen-containing compound, and a reducing agent into a chambercontaining the substrate.
 18. The method of claim 15, wherein thefluorine-free tungsten precursor is an organo-tungsten precursor. 19.The method of claim 15, further comprising depositing a first tungstenlayer in the feature from a fluorine-containing tungsten precursor,wherein the fluorine-free tungsten nitride layer is deposited on thefirst tungsten layer.